linux_dsm_epyc7002/kernel/rcu/tree.c
Eric Dumazet cfcdef5e30 rcu: Allow rcu_do_batch() to dynamically adjust batch sizes
Bimodal behavior of rcu_do_batch() is not really suited to Google
applications like gfe servers.

When a process with millions of sockets exits, closing all files
queues two rcu callbacks per socket.

This eventually reaches the point where RCU enters an emergency
mode, where rcu_do_batch() do not return until whole queue is flushed.

Each rcu callback lasts at least 70 nsec, so with millions of
elements, we easily spend more than 100 msec without rescheduling.

Goal of this patch is to avoid the infamous message like following
"need_resched set for > 51999388 ns (52 ticks) without schedule"

We dynamically adjust the number of elements we process, instead
of 10 / INFINITE choices, we use a floor of ~1 % of current entries.

If the number is above 1000, we switch to a time based limit of 3 msec
per batch, adjustable with /sys/module/rcutree/parameters/rcu_resched_ns

Signed-off-by: Eric Dumazet <edumazet@google.com>
[ paulmck: Forward-port and remove debug statements. ]
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-08-13 14:38:24 -07:00

3558 lines
114 KiB
C

// SPDX-License-Identifier: GPL-2.0+
/*
* Read-Copy Update mechanism for mutual exclusion
*
* Copyright IBM Corporation, 2008
*
* Authors: Dipankar Sarma <dipankar@in.ibm.com>
* Manfred Spraul <manfred@colorfullife.com>
* Paul E. McKenney <paulmck@linux.ibm.com> Hierarchical version
*
* Based on the original work by Paul McKenney <paulmck@linux.ibm.com>
* and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
*
* For detailed explanation of Read-Copy Update mechanism see -
* Documentation/RCU
*/
#define pr_fmt(fmt) "rcu: " fmt
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/spinlock.h>
#include <linux/smp.h>
#include <linux/rcupdate_wait.h>
#include <linux/interrupt.h>
#include <linux/sched.h>
#include <linux/sched/debug.h>
#include <linux/nmi.h>
#include <linux/atomic.h>
#include <linux/bitops.h>
#include <linux/export.h>
#include <linux/completion.h>
#include <linux/moduleparam.h>
#include <linux/percpu.h>
#include <linux/notifier.h>
#include <linux/cpu.h>
#include <linux/mutex.h>
#include <linux/time.h>
#include <linux/kernel_stat.h>
#include <linux/wait.h>
#include <linux/kthread.h>
#include <uapi/linux/sched/types.h>
#include <linux/prefetch.h>
#include <linux/delay.h>
#include <linux/stop_machine.h>
#include <linux/random.h>
#include <linux/trace_events.h>
#include <linux/suspend.h>
#include <linux/ftrace.h>
#include <linux/tick.h>
#include <linux/sysrq.h>
#include <linux/kprobes.h>
#include <linux/gfp.h>
#include <linux/oom.h>
#include <linux/smpboot.h>
#include <linux/jiffies.h>
#include <linux/sched/isolation.h>
#include <linux/sched/clock.h>
#include "../time/tick-internal.h"
#include "tree.h"
#include "rcu.h"
#ifdef MODULE_PARAM_PREFIX
#undef MODULE_PARAM_PREFIX
#endif
#define MODULE_PARAM_PREFIX "rcutree."
/* Data structures. */
/*
* Steal a bit from the bottom of ->dynticks for idle entry/exit
* control. Initially this is for TLB flushing.
*/
#define RCU_DYNTICK_CTRL_MASK 0x1
#define RCU_DYNTICK_CTRL_CTR (RCU_DYNTICK_CTRL_MASK + 1)
#ifndef rcu_eqs_special_exit
#define rcu_eqs_special_exit() do { } while (0)
#endif
static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, rcu_data) = {
.dynticks_nesting = 1,
.dynticks_nmi_nesting = DYNTICK_IRQ_NONIDLE,
.dynticks = ATOMIC_INIT(RCU_DYNTICK_CTRL_CTR),
};
struct rcu_state rcu_state = {
.level = { &rcu_state.node[0] },
.gp_state = RCU_GP_IDLE,
.gp_seq = (0UL - 300UL) << RCU_SEQ_CTR_SHIFT,
.barrier_mutex = __MUTEX_INITIALIZER(rcu_state.barrier_mutex),
.name = RCU_NAME,
.abbr = RCU_ABBR,
.exp_mutex = __MUTEX_INITIALIZER(rcu_state.exp_mutex),
.exp_wake_mutex = __MUTEX_INITIALIZER(rcu_state.exp_wake_mutex),
.ofl_lock = __RAW_SPIN_LOCK_UNLOCKED(rcu_state.ofl_lock),
};
/* Dump rcu_node combining tree at boot to verify correct setup. */
static bool dump_tree;
module_param(dump_tree, bool, 0444);
/* By default, use RCU_SOFTIRQ instead of rcuc kthreads. */
static bool use_softirq = 1;
module_param(use_softirq, bool, 0444);
/* Control rcu_node-tree auto-balancing at boot time. */
static bool rcu_fanout_exact;
module_param(rcu_fanout_exact, bool, 0444);
/* Increase (but not decrease) the RCU_FANOUT_LEAF at boot time. */
static int rcu_fanout_leaf = RCU_FANOUT_LEAF;
module_param(rcu_fanout_leaf, int, 0444);
int rcu_num_lvls __read_mostly = RCU_NUM_LVLS;
/* Number of rcu_nodes at specified level. */
int num_rcu_lvl[] = NUM_RCU_LVL_INIT;
int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */
/*
* The rcu_scheduler_active variable is initialized to the value
* RCU_SCHEDULER_INACTIVE and transitions RCU_SCHEDULER_INIT just before the
* first task is spawned. So when this variable is RCU_SCHEDULER_INACTIVE,
* RCU can assume that there is but one task, allowing RCU to (for example)
* optimize synchronize_rcu() to a simple barrier(). When this variable
* is RCU_SCHEDULER_INIT, RCU must actually do all the hard work required
* to detect real grace periods. This variable is also used to suppress
* boot-time false positives from lockdep-RCU error checking. Finally, it
* transitions from RCU_SCHEDULER_INIT to RCU_SCHEDULER_RUNNING after RCU
* is fully initialized, including all of its kthreads having been spawned.
*/
int rcu_scheduler_active __read_mostly;
EXPORT_SYMBOL_GPL(rcu_scheduler_active);
/*
* The rcu_scheduler_fully_active variable transitions from zero to one
* during the early_initcall() processing, which is after the scheduler
* is capable of creating new tasks. So RCU processing (for example,
* creating tasks for RCU priority boosting) must be delayed until after
* rcu_scheduler_fully_active transitions from zero to one. We also
* currently delay invocation of any RCU callbacks until after this point.
*
* It might later prove better for people registering RCU callbacks during
* early boot to take responsibility for these callbacks, but one step at
* a time.
*/
static int rcu_scheduler_fully_active __read_mostly;
static void rcu_report_qs_rnp(unsigned long mask, struct rcu_node *rnp,
unsigned long gps, unsigned long flags);
static void rcu_init_new_rnp(struct rcu_node *rnp_leaf);
static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf);
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu);
static void invoke_rcu_core(void);
static void rcu_report_exp_rdp(struct rcu_data *rdp);
static void sync_sched_exp_online_cleanup(int cpu);
/* rcuc/rcub kthread realtime priority */
static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 1 : 0;
module_param(kthread_prio, int, 0444);
/* Delay in jiffies for grace-period initialization delays, debug only. */
static int gp_preinit_delay;
module_param(gp_preinit_delay, int, 0444);
static int gp_init_delay;
module_param(gp_init_delay, int, 0444);
static int gp_cleanup_delay;
module_param(gp_cleanup_delay, int, 0444);
/* Retrieve RCU kthreads priority for rcutorture */
int rcu_get_gp_kthreads_prio(void)
{
return kthread_prio;
}
EXPORT_SYMBOL_GPL(rcu_get_gp_kthreads_prio);
/*
* Number of grace periods between delays, normalized by the duration of
* the delay. The longer the delay, the more the grace periods between
* each delay. The reason for this normalization is that it means that,
* for non-zero delays, the overall slowdown of grace periods is constant
* regardless of the duration of the delay. This arrangement balances
* the need for long delays to increase some race probabilities with the
* need for fast grace periods to increase other race probabilities.
*/
#define PER_RCU_NODE_PERIOD 3 /* Number of grace periods between delays. */
/*
* Compute the mask of online CPUs for the specified rcu_node structure.
* This will not be stable unless the rcu_node structure's ->lock is
* held, but the bit corresponding to the current CPU will be stable
* in most contexts.
*/
unsigned long rcu_rnp_online_cpus(struct rcu_node *rnp)
{
return READ_ONCE(rnp->qsmaskinitnext);
}
/*
* Return true if an RCU grace period is in progress. The READ_ONCE()s
* permit this function to be invoked without holding the root rcu_node
* structure's ->lock, but of course results can be subject to change.
*/
static int rcu_gp_in_progress(void)
{
return rcu_seq_state(rcu_seq_current(&rcu_state.gp_seq));
}
/*
* Return the number of callbacks queued on the specified CPU.
* Handles both the nocbs and normal cases.
*/
static long rcu_get_n_cbs_cpu(int cpu)
{
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
if (rcu_segcblist_is_enabled(&rdp->cblist))
return rcu_segcblist_n_cbs(&rdp->cblist);
return 0;
}
void rcu_softirq_qs(void)
{
rcu_qs();
rcu_preempt_deferred_qs(current);
}
/*
* Record entry into an extended quiescent state. This is only to be
* called when not already in an extended quiescent state.
*/
static void rcu_dynticks_eqs_enter(void)
{
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
int seq;
/*
* CPUs seeing atomic_add_return() must see prior RCU read-side
* critical sections, and we also must force ordering with the
* next idle sojourn.
*/
seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks);
/* Better be in an extended quiescent state! */
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
(seq & RCU_DYNTICK_CTRL_CTR));
/* Better not have special action (TLB flush) pending! */
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
(seq & RCU_DYNTICK_CTRL_MASK));
}
/*
* Record exit from an extended quiescent state. This is only to be
* called from an extended quiescent state.
*/
static void rcu_dynticks_eqs_exit(void)
{
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
int seq;
/*
* CPUs seeing atomic_add_return() must see prior idle sojourns,
* and we also must force ordering with the next RCU read-side
* critical section.
*/
seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks);
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
!(seq & RCU_DYNTICK_CTRL_CTR));
if (seq & RCU_DYNTICK_CTRL_MASK) {
atomic_andnot(RCU_DYNTICK_CTRL_MASK, &rdp->dynticks);
smp_mb__after_atomic(); /* _exit after clearing mask. */
/* Prefer duplicate flushes to losing a flush. */
rcu_eqs_special_exit();
}
}
/*
* Reset the current CPU's ->dynticks counter to indicate that the
* newly onlined CPU is no longer in an extended quiescent state.
* This will either leave the counter unchanged, or increment it
* to the next non-quiescent value.
*
* The non-atomic test/increment sequence works because the upper bits
* of the ->dynticks counter are manipulated only by the corresponding CPU,
* or when the corresponding CPU is offline.
*/
static void rcu_dynticks_eqs_online(void)
{
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
if (atomic_read(&rdp->dynticks) & RCU_DYNTICK_CTRL_CTR)
return;
atomic_add(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks);
}
/*
* Is the current CPU in an extended quiescent state?
*
* No ordering, as we are sampling CPU-local information.
*/
bool rcu_dynticks_curr_cpu_in_eqs(void)
{
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
return !(atomic_read(&rdp->dynticks) & RCU_DYNTICK_CTRL_CTR);
}
/*
* Snapshot the ->dynticks counter with full ordering so as to allow
* stable comparison of this counter with past and future snapshots.
*/
int rcu_dynticks_snap(struct rcu_data *rdp)
{
int snap = atomic_add_return(0, &rdp->dynticks);
return snap & ~RCU_DYNTICK_CTRL_MASK;
}
/*
* Return true if the snapshot returned from rcu_dynticks_snap()
* indicates that RCU is in an extended quiescent state.
*/
static bool rcu_dynticks_in_eqs(int snap)
{
return !(snap & RCU_DYNTICK_CTRL_CTR);
}
/*
* Return true if the CPU corresponding to the specified rcu_data
* structure has spent some time in an extended quiescent state since
* rcu_dynticks_snap() returned the specified snapshot.
*/
static bool rcu_dynticks_in_eqs_since(struct rcu_data *rdp, int snap)
{
return snap != rcu_dynticks_snap(rdp);
}
/*
* Set the special (bottom) bit of the specified CPU so that it
* will take special action (such as flushing its TLB) on the
* next exit from an extended quiescent state. Returns true if
* the bit was successfully set, or false if the CPU was not in
* an extended quiescent state.
*/
bool rcu_eqs_special_set(int cpu)
{
int old;
int new;
struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
do {
old = atomic_read(&rdp->dynticks);
if (old & RCU_DYNTICK_CTRL_CTR)
return false;
new = old | RCU_DYNTICK_CTRL_MASK;
} while (atomic_cmpxchg(&rdp->dynticks, old, new) != old);
return true;
}
/*
* Let the RCU core know that this CPU has gone through the scheduler,
* which is a quiescent state. This is called when the need for a
* quiescent state is urgent, so we burn an atomic operation and full
* memory barriers to let the RCU core know about it, regardless of what
* this CPU might (or might not) do in the near future.
*
* We inform the RCU core by emulating a zero-duration dyntick-idle period.
*
* The caller must have disabled interrupts and must not be idle.
*/
static void __maybe_unused rcu_momentary_dyntick_idle(void)
{
int special;
raw_cpu_write(rcu_data.rcu_need_heavy_qs, false);
special = atomic_add_return(2 * RCU_DYNTICK_CTRL_CTR,
&this_cpu_ptr(&rcu_data)->dynticks);
/* It is illegal to call this from idle state. */
WARN_ON_ONCE(!(special & RCU_DYNTICK_CTRL_CTR));
rcu_preempt_deferred_qs(current);
}
/**
* rcu_is_cpu_rrupt_from_idle - see if interrupted from idle
*
* If the current CPU is idle and running at a first-level (not nested)
* interrupt from idle, return true. The caller must have at least
* disabled preemption.
*/
static int rcu_is_cpu_rrupt_from_idle(void)
{
/* Called only from within the scheduling-clock interrupt */
lockdep_assert_in_irq();
/* Check for counter underflows */
RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nesting) < 0,
"RCU dynticks_nesting counter underflow!");
RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nmi_nesting) <= 0,
"RCU dynticks_nmi_nesting counter underflow/zero!");
/* Are we at first interrupt nesting level? */
if (__this_cpu_read(rcu_data.dynticks_nmi_nesting) != 1)
return false;
/* Does CPU appear to be idle from an RCU standpoint? */
return __this_cpu_read(rcu_data.dynticks_nesting) == 0;
}
#define DEFAULT_RCU_BLIMIT 10 /* Maximum callbacks per rcu_do_batch ... */
#define DEFAULT_MAX_RCU_BLIMIT 10000 /* ... even during callback flood. */
static long blimit = DEFAULT_RCU_BLIMIT;
#define DEFAULT_RCU_QHIMARK 10000 /* If this many pending, ignore blimit. */
static long qhimark = DEFAULT_RCU_QHIMARK;
#define DEFAULT_RCU_QLOMARK 100 /* Once only this many pending, use blimit. */
static long qlowmark = DEFAULT_RCU_QLOMARK;
module_param(blimit, long, 0444);
module_param(qhimark, long, 0444);
module_param(qlowmark, long, 0444);
static ulong jiffies_till_first_fqs = ULONG_MAX;
static ulong jiffies_till_next_fqs = ULONG_MAX;
static bool rcu_kick_kthreads;
static int rcu_divisor = 7;
module_param(rcu_divisor, int, 0644);
/* Force an exit from rcu_do_batch() after 3 milliseconds. */
static long rcu_resched_ns = 3 * NSEC_PER_MSEC;
module_param(rcu_resched_ns, long, 0644);
/*
* How long the grace period must be before we start recruiting
* quiescent-state help from rcu_note_context_switch().
*/
static ulong jiffies_till_sched_qs = ULONG_MAX;
module_param(jiffies_till_sched_qs, ulong, 0444);
static ulong jiffies_to_sched_qs; /* See adjust_jiffies_till_sched_qs(). */
module_param(jiffies_to_sched_qs, ulong, 0444); /* Display only! */
/*
* Make sure that we give the grace-period kthread time to detect any
* idle CPUs before taking active measures to force quiescent states.
* However, don't go below 100 milliseconds, adjusted upwards for really
* large systems.
*/
static void adjust_jiffies_till_sched_qs(void)
{
unsigned long j;
/* If jiffies_till_sched_qs was specified, respect the request. */
if (jiffies_till_sched_qs != ULONG_MAX) {
WRITE_ONCE(jiffies_to_sched_qs, jiffies_till_sched_qs);
return;
}
/* Otherwise, set to third fqs scan, but bound below on large system. */
j = READ_ONCE(jiffies_till_first_fqs) +
2 * READ_ONCE(jiffies_till_next_fqs);
if (j < HZ / 10 + nr_cpu_ids / RCU_JIFFIES_FQS_DIV)
j = HZ / 10 + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
pr_info("RCU calculated value of scheduler-enlistment delay is %ld jiffies.\n", j);
WRITE_ONCE(jiffies_to_sched_qs, j);
}
static int param_set_first_fqs_jiffies(const char *val, const struct kernel_param *kp)
{
ulong j;
int ret = kstrtoul(val, 0, &j);
if (!ret) {
WRITE_ONCE(*(ulong *)kp->arg, (j > HZ) ? HZ : j);
adjust_jiffies_till_sched_qs();
}
return ret;
}
static int param_set_next_fqs_jiffies(const char *val, const struct kernel_param *kp)
{
ulong j;
int ret = kstrtoul(val, 0, &j);
if (!ret) {
WRITE_ONCE(*(ulong *)kp->arg, (j > HZ) ? HZ : (j ?: 1));
adjust_jiffies_till_sched_qs();
}
return ret;
}
static struct kernel_param_ops first_fqs_jiffies_ops = {
.set = param_set_first_fqs_jiffies,
.get = param_get_ulong,
};
static struct kernel_param_ops next_fqs_jiffies_ops = {
.set = param_set_next_fqs_jiffies,
.get = param_get_ulong,
};
module_param_cb(jiffies_till_first_fqs, &first_fqs_jiffies_ops, &jiffies_till_first_fqs, 0644);
module_param_cb(jiffies_till_next_fqs, &next_fqs_jiffies_ops, &jiffies_till_next_fqs, 0644);
module_param(rcu_kick_kthreads, bool, 0644);
static void force_qs_rnp(int (*f)(struct rcu_data *rdp));
static int rcu_pending(void);
/*
* Return the number of RCU GPs completed thus far for debug & stats.
*/
unsigned long rcu_get_gp_seq(void)
{
return READ_ONCE(rcu_state.gp_seq);
}
EXPORT_SYMBOL_GPL(rcu_get_gp_seq);
/*
* Return the number of RCU expedited batches completed thus far for
* debug & stats. Odd numbers mean that a batch is in progress, even
* numbers mean idle. The value returned will thus be roughly double
* the cumulative batches since boot.
*/
unsigned long rcu_exp_batches_completed(void)
{
return rcu_state.expedited_sequence;
}
EXPORT_SYMBOL_GPL(rcu_exp_batches_completed);
/*
* Return the root node of the rcu_state structure.
*/
static struct rcu_node *rcu_get_root(void)
{
return &rcu_state.node[0];
}
/*
* Convert a ->gp_state value to a character string.
*/
static const char *gp_state_getname(short gs)
{
if (gs < 0 || gs >= ARRAY_SIZE(gp_state_names))
return "???";
return gp_state_names[gs];
}
/*
* Send along grace-period-related data for rcutorture diagnostics.
*/
void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
unsigned long *gp_seq)
{
switch (test_type) {
case RCU_FLAVOR:
*flags = READ_ONCE(rcu_state.gp_flags);
*gp_seq = rcu_seq_current(&rcu_state.gp_seq);
break;
default:
break;
}
}
EXPORT_SYMBOL_GPL(rcutorture_get_gp_data);
/*
* Enter an RCU extended quiescent state, which can be either the
* idle loop or adaptive-tickless usermode execution.
*
* We crowbar the ->dynticks_nmi_nesting field to zero to allow for
* the possibility of usermode upcalls having messed up our count
* of interrupt nesting level during the prior busy period.
*/
static void rcu_eqs_enter(bool user)
{
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
WARN_ON_ONCE(rdp->dynticks_nmi_nesting != DYNTICK_IRQ_NONIDLE);
WRITE_ONCE(rdp->dynticks_nmi_nesting, 0);
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
rdp->dynticks_nesting == 0);
if (rdp->dynticks_nesting != 1) {
rdp->dynticks_nesting--;
return;
}
lockdep_assert_irqs_disabled();
trace_rcu_dyntick(TPS("Start"), rdp->dynticks_nesting, 0, rdp->dynticks);
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
rdp = this_cpu_ptr(&rcu_data);
do_nocb_deferred_wakeup(rdp);
rcu_prepare_for_idle();
rcu_preempt_deferred_qs(current);
WRITE_ONCE(rdp->dynticks_nesting, 0); /* Avoid irq-access tearing. */
rcu_dynticks_eqs_enter();
rcu_dynticks_task_enter();
}
/**
* rcu_idle_enter - inform RCU that current CPU is entering idle
*
* Enter idle mode, in other words, -leave- the mode in which RCU
* read-side critical sections can occur. (Though RCU read-side
* critical sections can occur in irq handlers in idle, a possibility
* handled by irq_enter() and irq_exit().)
*
* If you add or remove a call to rcu_idle_enter(), be sure to test with
* CONFIG_RCU_EQS_DEBUG=y.
*/
void rcu_idle_enter(void)
{
lockdep_assert_irqs_disabled();
rcu_eqs_enter(false);
}
#ifdef CONFIG_NO_HZ_FULL
/**
* rcu_user_enter - inform RCU that we are resuming userspace.
*
* Enter RCU idle mode right before resuming userspace. No use of RCU
* is permitted between this call and rcu_user_exit(). This way the
* CPU doesn't need to maintain the tick for RCU maintenance purposes
* when the CPU runs in userspace.
*
* If you add or remove a call to rcu_user_enter(), be sure to test with
* CONFIG_RCU_EQS_DEBUG=y.
*/
void rcu_user_enter(void)
{
lockdep_assert_irqs_disabled();
rcu_eqs_enter(true);
}
#endif /* CONFIG_NO_HZ_FULL */
/*
* If we are returning from the outermost NMI handler that interrupted an
* RCU-idle period, update rdp->dynticks and rdp->dynticks_nmi_nesting
* to let the RCU grace-period handling know that the CPU is back to
* being RCU-idle.
*
* If you add or remove a call to rcu_nmi_exit_common(), be sure to test
* with CONFIG_RCU_EQS_DEBUG=y.
*/
static __always_inline void rcu_nmi_exit_common(bool irq)
{
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
/*
* Check for ->dynticks_nmi_nesting underflow and bad ->dynticks.
* (We are exiting an NMI handler, so RCU better be paying attention
* to us!)
*/
WARN_ON_ONCE(rdp->dynticks_nmi_nesting <= 0);
WARN_ON_ONCE(rcu_dynticks_curr_cpu_in_eqs());
/*
* If the nesting level is not 1, the CPU wasn't RCU-idle, so
* leave it in non-RCU-idle state.
*/
if (rdp->dynticks_nmi_nesting != 1) {
trace_rcu_dyntick(TPS("--="), rdp->dynticks_nmi_nesting, rdp->dynticks_nmi_nesting - 2, rdp->dynticks);
WRITE_ONCE(rdp->dynticks_nmi_nesting, /* No store tearing. */
rdp->dynticks_nmi_nesting - 2);
return;
}
/* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
trace_rcu_dyntick(TPS("Startirq"), rdp->dynticks_nmi_nesting, 0, rdp->dynticks);
WRITE_ONCE(rdp->dynticks_nmi_nesting, 0); /* Avoid store tearing. */
if (irq)
rcu_prepare_for_idle();
rcu_dynticks_eqs_enter();
if (irq)
rcu_dynticks_task_enter();
}
/**
* rcu_nmi_exit - inform RCU of exit from NMI context
*
* If you add or remove a call to rcu_nmi_exit(), be sure to test
* with CONFIG_RCU_EQS_DEBUG=y.
*/
void rcu_nmi_exit(void)
{
rcu_nmi_exit_common(false);
}
/**
* rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
*
* Exit from an interrupt handler, which might possibly result in entering
* idle mode, in other words, leaving the mode in which read-side critical
* sections can occur. The caller must have disabled interrupts.
*
* This code assumes that the idle loop never does anything that might
* result in unbalanced calls to irq_enter() and irq_exit(). If your
* architecture's idle loop violates this assumption, RCU will give you what
* you deserve, good and hard. But very infrequently and irreproducibly.
*
* Use things like work queues to work around this limitation.
*
* You have been warned.
*
* If you add or remove a call to rcu_irq_exit(), be sure to test with
* CONFIG_RCU_EQS_DEBUG=y.
*/
void rcu_irq_exit(void)
{
lockdep_assert_irqs_disabled();
rcu_nmi_exit_common(true);
}
/*
* Wrapper for rcu_irq_exit() where interrupts are enabled.
*
* If you add or remove a call to rcu_irq_exit_irqson(), be sure to test
* with CONFIG_RCU_EQS_DEBUG=y.
*/
void rcu_irq_exit_irqson(void)
{
unsigned long flags;
local_irq_save(flags);
rcu_irq_exit();
local_irq_restore(flags);
}
/*
* Exit an RCU extended quiescent state, which can be either the
* idle loop or adaptive-tickless usermode execution.
*
* We crowbar the ->dynticks_nmi_nesting field to DYNTICK_IRQ_NONIDLE to
* allow for the possibility of usermode upcalls messing up our count of
* interrupt nesting level during the busy period that is just now starting.
*/
static void rcu_eqs_exit(bool user)
{
struct rcu_data *rdp;
long oldval;
lockdep_assert_irqs_disabled();
rdp = this_cpu_ptr(&rcu_data);
oldval = rdp->dynticks_nesting;
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && oldval < 0);
if (oldval) {
rdp->dynticks_nesting++;
return;
}
rcu_dynticks_task_exit();
rcu_dynticks_eqs_exit();
rcu_cleanup_after_idle();
trace_rcu_dyntick(TPS("End"), rdp->dynticks_nesting, 1, rdp->dynticks);
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
WRITE_ONCE(rdp->dynticks_nesting, 1);
WARN_ON_ONCE(rdp->dynticks_nmi_nesting);
WRITE_ONCE(rdp->dynticks_nmi_nesting, DYNTICK_IRQ_NONIDLE);
}
/**
* rcu_idle_exit - inform RCU that current CPU is leaving idle
*
* Exit idle mode, in other words, -enter- the mode in which RCU
* read-side critical sections can occur.
*
* If you add or remove a call to rcu_idle_exit(), be sure to test with
* CONFIG_RCU_EQS_DEBUG=y.
*/
void rcu_idle_exit(void)
{
unsigned long flags;
local_irq_save(flags);
rcu_eqs_exit(false);
local_irq_restore(flags);
}
#ifdef CONFIG_NO_HZ_FULL
/**
* rcu_user_exit - inform RCU that we are exiting userspace.
*
* Exit RCU idle mode while entering the kernel because it can
* run a RCU read side critical section anytime.
*
* If you add or remove a call to rcu_user_exit(), be sure to test with
* CONFIG_RCU_EQS_DEBUG=y.
*/
void rcu_user_exit(void)
{
rcu_eqs_exit(1);
}
#endif /* CONFIG_NO_HZ_FULL */
/**
* rcu_nmi_enter_common - inform RCU of entry to NMI context
* @irq: Is this call from rcu_irq_enter?
*
* If the CPU was idle from RCU's viewpoint, update rdp->dynticks and
* rdp->dynticks_nmi_nesting to let the RCU grace-period handling know
* that the CPU is active. This implementation permits nested NMIs, as
* long as the nesting level does not overflow an int. (You will probably
* run out of stack space first.)
*
* If you add or remove a call to rcu_nmi_enter_common(), be sure to test
* with CONFIG_RCU_EQS_DEBUG=y.
*/
static __always_inline void rcu_nmi_enter_common(bool irq)
{
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
long incby = 2;
/* Complain about underflow. */
WARN_ON_ONCE(rdp->dynticks_nmi_nesting < 0);
/*
* If idle from RCU viewpoint, atomically increment ->dynticks
* to mark non-idle and increment ->dynticks_nmi_nesting by one.
* Otherwise, increment ->dynticks_nmi_nesting by two. This means
* if ->dynticks_nmi_nesting is equal to one, we are guaranteed
* to be in the outermost NMI handler that interrupted an RCU-idle
* period (observation due to Andy Lutomirski).
*/
if (rcu_dynticks_curr_cpu_in_eqs()) {
if (irq)
rcu_dynticks_task_exit();
rcu_dynticks_eqs_exit();
if (irq)
rcu_cleanup_after_idle();
incby = 1;
}
trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="),
rdp->dynticks_nmi_nesting,
rdp->dynticks_nmi_nesting + incby, rdp->dynticks);
WRITE_ONCE(rdp->dynticks_nmi_nesting, /* Prevent store tearing. */
rdp->dynticks_nmi_nesting + incby);
barrier();
}
/**
* rcu_nmi_enter - inform RCU of entry to NMI context
*/
void rcu_nmi_enter(void)
{
rcu_nmi_enter_common(false);
}
NOKPROBE_SYMBOL(rcu_nmi_enter);
/**
* rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
*
* Enter an interrupt handler, which might possibly result in exiting
* idle mode, in other words, entering the mode in which read-side critical
* sections can occur. The caller must have disabled interrupts.
*
* Note that the Linux kernel is fully capable of entering an interrupt
* handler that it never exits, for example when doing upcalls to user mode!
* This code assumes that the idle loop never does upcalls to user mode.
* If your architecture's idle loop does do upcalls to user mode (or does
* anything else that results in unbalanced calls to the irq_enter() and
* irq_exit() functions), RCU will give you what you deserve, good and hard.
* But very infrequently and irreproducibly.
*
* Use things like work queues to work around this limitation.
*
* You have been warned.
*
* If you add or remove a call to rcu_irq_enter(), be sure to test with
* CONFIG_RCU_EQS_DEBUG=y.
*/
void rcu_irq_enter(void)
{
lockdep_assert_irqs_disabled();
rcu_nmi_enter_common(true);
}
/*
* Wrapper for rcu_irq_enter() where interrupts are enabled.
*
* If you add or remove a call to rcu_irq_enter_irqson(), be sure to test
* with CONFIG_RCU_EQS_DEBUG=y.
*/
void rcu_irq_enter_irqson(void)
{
unsigned long flags;
local_irq_save(flags);
rcu_irq_enter();
local_irq_restore(flags);
}
/**
* rcu_is_watching - see if RCU thinks that the current CPU is not idle
*
* Return true if RCU is watching the running CPU, which means that this
* CPU can safely enter RCU read-side critical sections. In other words,
* if the current CPU is not in its idle loop or is in an interrupt or
* NMI handler, return true.
*/
bool notrace rcu_is_watching(void)
{
bool ret;
preempt_disable_notrace();
ret = !rcu_dynticks_curr_cpu_in_eqs();
preempt_enable_notrace();
return ret;
}
EXPORT_SYMBOL_GPL(rcu_is_watching);
/*
* If a holdout task is actually running, request an urgent quiescent
* state from its CPU. This is unsynchronized, so migrations can cause
* the request to go to the wrong CPU. Which is OK, all that will happen
* is that the CPU's next context switch will be a bit slower and next
* time around this task will generate another request.
*/
void rcu_request_urgent_qs_task(struct task_struct *t)
{
int cpu;
barrier();
cpu = task_cpu(t);
if (!task_curr(t))
return; /* This task is not running on that CPU. */
smp_store_release(per_cpu_ptr(&rcu_data.rcu_urgent_qs, cpu), true);
}
#if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
/*
* Is the current CPU online as far as RCU is concerned?
*
* Disable preemption to avoid false positives that could otherwise
* happen due to the current CPU number being sampled, this task being
* preempted, its old CPU being taken offline, resuming on some other CPU,
* then determining that its old CPU is now offline.
*
* Disable checking if in an NMI handler because we cannot safely
* report errors from NMI handlers anyway. In addition, it is OK to use
* RCU on an offline processor during initial boot, hence the check for
* rcu_scheduler_fully_active.
*/
bool rcu_lockdep_current_cpu_online(void)
{
struct rcu_data *rdp;
struct rcu_node *rnp;
bool ret = false;
if (in_nmi() || !rcu_scheduler_fully_active)
return true;
preempt_disable();
rdp = this_cpu_ptr(&rcu_data);
rnp = rdp->mynode;
if (rdp->grpmask & rcu_rnp_online_cpus(rnp))
ret = true;
preempt_enable();
return ret;
}
EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
#endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
/*
* We are reporting a quiescent state on behalf of some other CPU, so
* it is our responsibility to check for and handle potential overflow
* of the rcu_node ->gp_seq counter with respect to the rcu_data counters.
* After all, the CPU might be in deep idle state, and thus executing no
* code whatsoever.
*/
static void rcu_gpnum_ovf(struct rcu_node *rnp, struct rcu_data *rdp)
{
raw_lockdep_assert_held_rcu_node(rnp);
if (ULONG_CMP_LT(rcu_seq_current(&rdp->gp_seq) + ULONG_MAX / 4,
rnp->gp_seq))
WRITE_ONCE(rdp->gpwrap, true);
if (ULONG_CMP_LT(rdp->rcu_iw_gp_seq + ULONG_MAX / 4, rnp->gp_seq))
rdp->rcu_iw_gp_seq = rnp->gp_seq + ULONG_MAX / 4;
}
/*
* Snapshot the specified CPU's dynticks counter so that we can later
* credit them with an implicit quiescent state. Return 1 if this CPU
* is in dynticks idle mode, which is an extended quiescent state.
*/
static int dyntick_save_progress_counter(struct rcu_data *rdp)
{
rdp->dynticks_snap = rcu_dynticks_snap(rdp);
if (rcu_dynticks_in_eqs(rdp->dynticks_snap)) {
trace_rcu_fqs(rcu_state.name, rdp->gp_seq, rdp->cpu, TPS("dti"));
rcu_gpnum_ovf(rdp->mynode, rdp);
return 1;
}
return 0;
}
/*
* Return true if the specified CPU has passed through a quiescent
* state by virtue of being in or having passed through an dynticks
* idle state since the last call to dyntick_save_progress_counter()
* for this same CPU, or by virtue of having been offline.
*/
static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
{
unsigned long jtsq;
bool *rnhqp;
bool *ruqp;
struct rcu_node *rnp = rdp->mynode;
/*
* If the CPU passed through or entered a dynticks idle phase with
* no active irq/NMI handlers, then we can safely pretend that the CPU
* already acknowledged the request to pass through a quiescent
* state. Either way, that CPU cannot possibly be in an RCU
* read-side critical section that started before the beginning
* of the current RCU grace period.
*/
if (rcu_dynticks_in_eqs_since(rdp, rdp->dynticks_snap)) {
trace_rcu_fqs(rcu_state.name, rdp->gp_seq, rdp->cpu, TPS("dti"));
rcu_gpnum_ovf(rnp, rdp);
return 1;
}
/* If waiting too long on an offline CPU, complain. */
if (!(rdp->grpmask & rcu_rnp_online_cpus(rnp)) &&
time_after(jiffies, rcu_state.gp_start + HZ)) {
bool onl;
struct rcu_node *rnp1;
WARN_ON(1); /* Offline CPUs are supposed to report QS! */
pr_info("%s: grp: %d-%d level: %d ->gp_seq %ld ->completedqs %ld\n",
__func__, rnp->grplo, rnp->grphi, rnp->level,
(long)rnp->gp_seq, (long)rnp->completedqs);
for (rnp1 = rnp; rnp1; rnp1 = rnp1->parent)
pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx ->rcu_gp_init_mask %#lx\n",
__func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext, rnp1->rcu_gp_init_mask);
onl = !!(rdp->grpmask & rcu_rnp_online_cpus(rnp));
pr_info("%s %d: %c online: %ld(%d) offline: %ld(%d)\n",
__func__, rdp->cpu, ".o"[onl],
(long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_flags,
(long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_flags);
return 1; /* Break things loose after complaining. */
}
/*
* A CPU running for an extended time within the kernel can
* delay RCU grace periods: (1) At age jiffies_to_sched_qs,
* set .rcu_urgent_qs, (2) At age 2*jiffies_to_sched_qs, set
* both .rcu_need_heavy_qs and .rcu_urgent_qs. Note that the
* unsynchronized assignments to the per-CPU rcu_need_heavy_qs
* variable are safe because the assignments are repeated if this
* CPU failed to pass through a quiescent state. This code
* also checks .jiffies_resched in case jiffies_to_sched_qs
* is set way high.
*/
jtsq = READ_ONCE(jiffies_to_sched_qs);
ruqp = per_cpu_ptr(&rcu_data.rcu_urgent_qs, rdp->cpu);
rnhqp = &per_cpu(rcu_data.rcu_need_heavy_qs, rdp->cpu);
if (!READ_ONCE(*rnhqp) &&
(time_after(jiffies, rcu_state.gp_start + jtsq * 2) ||
time_after(jiffies, rcu_state.jiffies_resched))) {
WRITE_ONCE(*rnhqp, true);
/* Store rcu_need_heavy_qs before rcu_urgent_qs. */
smp_store_release(ruqp, true);
} else if (time_after(jiffies, rcu_state.gp_start + jtsq)) {
WRITE_ONCE(*ruqp, true);
}
/*
* NO_HZ_FULL CPUs can run in-kernel without rcu_sched_clock_irq!
* The above code handles this, but only for straight cond_resched().
* And some in-kernel loops check need_resched() before calling
* cond_resched(), which defeats the above code for CPUs that are
* running in-kernel with scheduling-clock interrupts disabled.
* So hit them over the head with the resched_cpu() hammer!
*/
if (tick_nohz_full_cpu(rdp->cpu) &&
time_after(jiffies,
READ_ONCE(rdp->last_fqs_resched) + jtsq * 3)) {
resched_cpu(rdp->cpu);
WRITE_ONCE(rdp->last_fqs_resched, jiffies);
}
/*
* If more than halfway to RCU CPU stall-warning time, invoke
* resched_cpu() more frequently to try to loosen things up a bit.
* Also check to see if the CPU is getting hammered with interrupts,
* but only once per grace period, just to keep the IPIs down to
* a dull roar.
*/
if (time_after(jiffies, rcu_state.jiffies_resched)) {
if (time_after(jiffies,
READ_ONCE(rdp->last_fqs_resched) + jtsq)) {
resched_cpu(rdp->cpu);
WRITE_ONCE(rdp->last_fqs_resched, jiffies);
}
if (IS_ENABLED(CONFIG_IRQ_WORK) &&
!rdp->rcu_iw_pending && rdp->rcu_iw_gp_seq != rnp->gp_seq &&
(rnp->ffmask & rdp->grpmask)) {
init_irq_work(&rdp->rcu_iw, rcu_iw_handler);
rdp->rcu_iw_pending = true;
rdp->rcu_iw_gp_seq = rnp->gp_seq;
irq_work_queue_on(&rdp->rcu_iw, rdp->cpu);
}
}
return 0;
}
/* Trace-event wrapper function for trace_rcu_future_grace_period. */
static void trace_rcu_this_gp(struct rcu_node *rnp, struct rcu_data *rdp,
unsigned long gp_seq_req, const char *s)
{
trace_rcu_future_grace_period(rcu_state.name, rnp->gp_seq, gp_seq_req,
rnp->level, rnp->grplo, rnp->grphi, s);
}
/*
* rcu_start_this_gp - Request the start of a particular grace period
* @rnp_start: The leaf node of the CPU from which to start.
* @rdp: The rcu_data corresponding to the CPU from which to start.
* @gp_seq_req: The gp_seq of the grace period to start.
*
* Start the specified grace period, as needed to handle newly arrived
* callbacks. The required future grace periods are recorded in each
* rcu_node structure's ->gp_seq_needed field. Returns true if there
* is reason to awaken the grace-period kthread.
*
* The caller must hold the specified rcu_node structure's ->lock, which
* is why the caller is responsible for waking the grace-period kthread.
*
* Returns true if the GP thread needs to be awakened else false.
*/
static bool rcu_start_this_gp(struct rcu_node *rnp_start, struct rcu_data *rdp,
unsigned long gp_seq_req)
{
bool ret = false;
struct rcu_node *rnp;
/*
* Use funnel locking to either acquire the root rcu_node
* structure's lock or bail out if the need for this grace period
* has already been recorded -- or if that grace period has in
* fact already started. If there is already a grace period in
* progress in a non-leaf node, no recording is needed because the
* end of the grace period will scan the leaf rcu_node structures.
* Note that rnp_start->lock must not be released.
*/
raw_lockdep_assert_held_rcu_node(rnp_start);
trace_rcu_this_gp(rnp_start, rdp, gp_seq_req, TPS("Startleaf"));
for (rnp = rnp_start; 1; rnp = rnp->parent) {
if (rnp != rnp_start)
raw_spin_lock_rcu_node(rnp);
if (ULONG_CMP_GE(rnp->gp_seq_needed, gp_seq_req) ||
rcu_seq_started(&rnp->gp_seq, gp_seq_req) ||
(rnp != rnp_start &&
rcu_seq_state(rcu_seq_current(&rnp->gp_seq)))) {
trace_rcu_this_gp(rnp, rdp, gp_seq_req,
TPS("Prestarted"));
goto unlock_out;
}
rnp->gp_seq_needed = gp_seq_req;
if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq))) {
/*
* We just marked the leaf or internal node, and a
* grace period is in progress, which means that
* rcu_gp_cleanup() will see the marking. Bail to
* reduce contention.
*/
trace_rcu_this_gp(rnp_start, rdp, gp_seq_req,
TPS("Startedleaf"));
goto unlock_out;
}
if (rnp != rnp_start && rnp->parent != NULL)
raw_spin_unlock_rcu_node(rnp);
if (!rnp->parent)
break; /* At root, and perhaps also leaf. */
}
/* If GP already in progress, just leave, otherwise start one. */
if (rcu_gp_in_progress()) {
trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedleafroot"));
goto unlock_out;
}
trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedroot"));
WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags | RCU_GP_FLAG_INIT);
rcu_state.gp_req_activity = jiffies;
if (!rcu_state.gp_kthread) {
trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("NoGPkthread"));
goto unlock_out;
}
trace_rcu_grace_period(rcu_state.name, READ_ONCE(rcu_state.gp_seq), TPS("newreq"));
ret = true; /* Caller must wake GP kthread. */
unlock_out:
/* Push furthest requested GP to leaf node and rcu_data structure. */
if (ULONG_CMP_LT(gp_seq_req, rnp->gp_seq_needed)) {
rnp_start->gp_seq_needed = rnp->gp_seq_needed;
rdp->gp_seq_needed = rnp->gp_seq_needed;
}
if (rnp != rnp_start)
raw_spin_unlock_rcu_node(rnp);
return ret;
}
/*
* Clean up any old requests for the just-ended grace period. Also return
* whether any additional grace periods have been requested.
*/
static bool rcu_future_gp_cleanup(struct rcu_node *rnp)
{
bool needmore;
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
needmore = ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed);
if (!needmore)
rnp->gp_seq_needed = rnp->gp_seq; /* Avoid counter wrap. */
trace_rcu_this_gp(rnp, rdp, rnp->gp_seq,
needmore ? TPS("CleanupMore") : TPS("Cleanup"));
return needmore;
}
/*
* Awaken the grace-period kthread. Don't do a self-awaken (unless in
* an interrupt or softirq handler), and don't bother awakening when there
* is nothing for the grace-period kthread to do (as in several CPUs raced
* to awaken, and we lost), and finally don't try to awaken a kthread that
* has not yet been created. If all those checks are passed, track some
* debug information and awaken.
*
* So why do the self-wakeup when in an interrupt or softirq handler
* in the grace-period kthread's context? Because the kthread might have
* been interrupted just as it was going to sleep, and just after the final
* pre-sleep check of the awaken condition. In this case, a wakeup really
* is required, and is therefore supplied.
*/
static void rcu_gp_kthread_wake(void)
{
if ((current == rcu_state.gp_kthread &&
!in_irq() && !in_serving_softirq()) ||
!READ_ONCE(rcu_state.gp_flags) ||
!rcu_state.gp_kthread)
return;
WRITE_ONCE(rcu_state.gp_wake_time, jiffies);
WRITE_ONCE(rcu_state.gp_wake_seq, READ_ONCE(rcu_state.gp_seq));
swake_up_one(&rcu_state.gp_wq);
}
/*
* If there is room, assign a ->gp_seq number to any callbacks on this
* CPU that have not already been assigned. Also accelerate any callbacks
* that were previously assigned a ->gp_seq number that has since proven
* to be too conservative, which can happen if callbacks get assigned a
* ->gp_seq number while RCU is idle, but with reference to a non-root
* rcu_node structure. This function is idempotent, so it does not hurt
* to call it repeatedly. Returns an flag saying that we should awaken
* the RCU grace-period kthread.
*
* The caller must hold rnp->lock with interrupts disabled.
*/
static bool rcu_accelerate_cbs(struct rcu_node *rnp, struct rcu_data *rdp)
{
unsigned long gp_seq_req;
bool ret = false;
rcu_lockdep_assert_cblist_protected(rdp);
raw_lockdep_assert_held_rcu_node(rnp);
/* If no pending (not yet ready to invoke) callbacks, nothing to do. */
if (!rcu_segcblist_pend_cbs(&rdp->cblist))
return false;
/*
* Callbacks are often registered with incomplete grace-period
* information. Something about the fact that getting exact
* information requires acquiring a global lock... RCU therefore
* makes a conservative estimate of the grace period number at which
* a given callback will become ready to invoke. The following
* code checks this estimate and improves it when possible, thus
* accelerating callback invocation to an earlier grace-period
* number.
*/
gp_seq_req = rcu_seq_snap(&rcu_state.gp_seq);
if (rcu_segcblist_accelerate(&rdp->cblist, gp_seq_req))
ret = rcu_start_this_gp(rnp, rdp, gp_seq_req);
/* Trace depending on how much we were able to accelerate. */
if (rcu_segcblist_restempty(&rdp->cblist, RCU_WAIT_TAIL))
trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("AccWaitCB"));
else
trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("AccReadyCB"));
return ret;
}
/*
* Similar to rcu_accelerate_cbs(), but does not require that the leaf
* rcu_node structure's ->lock be held. It consults the cached value
* of ->gp_seq_needed in the rcu_data structure, and if that indicates
* that a new grace-period request be made, invokes rcu_accelerate_cbs()
* while holding the leaf rcu_node structure's ->lock.
*/
static void rcu_accelerate_cbs_unlocked(struct rcu_node *rnp,
struct rcu_data *rdp)
{
unsigned long c;
bool needwake;
rcu_lockdep_assert_cblist_protected(rdp);
c = rcu_seq_snap(&rcu_state.gp_seq);
if (!rdp->gpwrap && ULONG_CMP_GE(rdp->gp_seq_needed, c)) {
/* Old request still live, so mark recent callbacks. */
(void)rcu_segcblist_accelerate(&rdp->cblist, c);
return;
}
raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
needwake = rcu_accelerate_cbs(rnp, rdp);
raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
if (needwake)
rcu_gp_kthread_wake();
}
/*
* Move any callbacks whose grace period has completed to the
* RCU_DONE_TAIL sublist, then compact the remaining sublists and
* assign ->gp_seq numbers to any callbacks in the RCU_NEXT_TAIL
* sublist. This function is idempotent, so it does not hurt to
* invoke it repeatedly. As long as it is not invoked -too- often...
* Returns true if the RCU grace-period kthread needs to be awakened.
*
* The caller must hold rnp->lock with interrupts disabled.
*/
static bool rcu_advance_cbs(struct rcu_node *rnp, struct rcu_data *rdp)
{
rcu_lockdep_assert_cblist_protected(rdp);
raw_lockdep_assert_held_rcu_node(rnp);
/* If no pending (not yet ready to invoke) callbacks, nothing to do. */
if (!rcu_segcblist_pend_cbs(&rdp->cblist))
return false;
/*
* Find all callbacks whose ->gp_seq numbers indicate that they
* are ready to invoke, and put them into the RCU_DONE_TAIL sublist.
*/
rcu_segcblist_advance(&rdp->cblist, rnp->gp_seq);
/* Classify any remaining callbacks. */
return rcu_accelerate_cbs(rnp, rdp);
}
/*
* Move and classify callbacks, but only if doing so won't require
* that the RCU grace-period kthread be awakened.
*/
static void __maybe_unused rcu_advance_cbs_nowake(struct rcu_node *rnp,
struct rcu_data *rdp)
{
rcu_lockdep_assert_cblist_protected(rdp);
if (!rcu_seq_state(rcu_seq_current(&rnp->gp_seq)) ||
!raw_spin_trylock_rcu_node(rnp))
return;
WARN_ON_ONCE(rcu_advance_cbs(rnp, rdp));
raw_spin_unlock_rcu_node(rnp);
}
/*
* Update CPU-local rcu_data state to record the beginnings and ends of
* grace periods. The caller must hold the ->lock of the leaf rcu_node
* structure corresponding to the current CPU, and must have irqs disabled.
* Returns true if the grace-period kthread needs to be awakened.
*/
static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp)
{
bool ret = false;
bool need_gp;
const bool offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
rcu_segcblist_is_offloaded(&rdp->cblist);
raw_lockdep_assert_held_rcu_node(rnp);
if (rdp->gp_seq == rnp->gp_seq)
return false; /* Nothing to do. */
/* Handle the ends of any preceding grace periods first. */
if (rcu_seq_completed_gp(rdp->gp_seq, rnp->gp_seq) ||
unlikely(READ_ONCE(rdp->gpwrap))) {
if (!offloaded)
ret = rcu_advance_cbs(rnp, rdp); /* Advance CBs. */
trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("cpuend"));
} else {
if (!offloaded)
ret = rcu_accelerate_cbs(rnp, rdp); /* Recent CBs. */
}
/* Now handle the beginnings of any new-to-this-CPU grace periods. */
if (rcu_seq_new_gp(rdp->gp_seq, rnp->gp_seq) ||
unlikely(READ_ONCE(rdp->gpwrap))) {
/*
* If the current grace period is waiting for this CPU,
* set up to detect a quiescent state, otherwise don't
* go looking for one.
*/
trace_rcu_grace_period(rcu_state.name, rnp->gp_seq, TPS("cpustart"));
need_gp = !!(rnp->qsmask & rdp->grpmask);
rdp->cpu_no_qs.b.norm = need_gp;
rdp->core_needs_qs = need_gp;
zero_cpu_stall_ticks(rdp);
}
rdp->gp_seq = rnp->gp_seq; /* Remember new grace-period state. */
if (ULONG_CMP_LT(rdp->gp_seq_needed, rnp->gp_seq_needed) || rdp->gpwrap)
rdp->gp_seq_needed = rnp->gp_seq_needed;
WRITE_ONCE(rdp->gpwrap, false);
rcu_gpnum_ovf(rnp, rdp);
return ret;
}
static void note_gp_changes(struct rcu_data *rdp)
{
unsigned long flags;
bool needwake;
struct rcu_node *rnp;
local_irq_save(flags);
rnp = rdp->mynode;
if ((rdp->gp_seq == rcu_seq_current(&rnp->gp_seq) &&
!unlikely(READ_ONCE(rdp->gpwrap))) || /* w/out lock. */
!raw_spin_trylock_rcu_node(rnp)) { /* irqs already off, so later. */
local_irq_restore(flags);
return;
}
needwake = __note_gp_changes(rnp, rdp);
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
if (needwake)
rcu_gp_kthread_wake();
}
static void rcu_gp_slow(int delay)
{
if (delay > 0 &&
!(rcu_seq_ctr(rcu_state.gp_seq) %
(rcu_num_nodes * PER_RCU_NODE_PERIOD * delay)))
schedule_timeout_uninterruptible(delay);
}
/*
* Initialize a new grace period. Return false if no grace period required.
*/
static bool rcu_gp_init(void)
{
unsigned long flags;
unsigned long oldmask;
unsigned long mask;
struct rcu_data *rdp;
struct rcu_node *rnp = rcu_get_root();
WRITE_ONCE(rcu_state.gp_activity, jiffies);
raw_spin_lock_irq_rcu_node(rnp);
if (!READ_ONCE(rcu_state.gp_flags)) {
/* Spurious wakeup, tell caller to go back to sleep. */
raw_spin_unlock_irq_rcu_node(rnp);
return false;
}
WRITE_ONCE(rcu_state.gp_flags, 0); /* Clear all flags: New GP. */
if (WARN_ON_ONCE(rcu_gp_in_progress())) {
/*
* Grace period already in progress, don't start another.
* Not supposed to be able to happen.
*/
raw_spin_unlock_irq_rcu_node(rnp);
return false;
}
/* Advance to a new grace period and initialize state. */
record_gp_stall_check_time();
/* Record GP times before starting GP, hence rcu_seq_start(). */
rcu_seq_start(&rcu_state.gp_seq);
trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("start"));
raw_spin_unlock_irq_rcu_node(rnp);
/*
* Apply per-leaf buffered online and offline operations to the
* rcu_node tree. Note that this new grace period need not wait
* for subsequent online CPUs, and that quiescent-state forcing
* will handle subsequent offline CPUs.
*/
rcu_state.gp_state = RCU_GP_ONOFF;
rcu_for_each_leaf_node(rnp) {
raw_spin_lock(&rcu_state.ofl_lock);
raw_spin_lock_irq_rcu_node(rnp);
if (rnp->qsmaskinit == rnp->qsmaskinitnext &&
!rnp->wait_blkd_tasks) {
/* Nothing to do on this leaf rcu_node structure. */
raw_spin_unlock_irq_rcu_node(rnp);
raw_spin_unlock(&rcu_state.ofl_lock);
continue;
}
/* Record old state, apply changes to ->qsmaskinit field. */
oldmask = rnp->qsmaskinit;
rnp->qsmaskinit = rnp->qsmaskinitnext;
/* If zero-ness of ->qsmaskinit changed, propagate up tree. */
if (!oldmask != !rnp->qsmaskinit) {
if (!oldmask) { /* First online CPU for rcu_node. */
if (!rnp->wait_blkd_tasks) /* Ever offline? */
rcu_init_new_rnp(rnp);
} else if (rcu_preempt_has_tasks(rnp)) {
rnp->wait_blkd_tasks = true; /* blocked tasks */
} else { /* Last offline CPU and can propagate. */
rcu_cleanup_dead_rnp(rnp);
}
}
/*
* If all waited-on tasks from prior grace period are
* done, and if all this rcu_node structure's CPUs are
* still offline, propagate up the rcu_node tree and
* clear ->wait_blkd_tasks. Otherwise, if one of this
* rcu_node structure's CPUs has since come back online,
* simply clear ->wait_blkd_tasks.
*/
if (rnp->wait_blkd_tasks &&
(!rcu_preempt_has_tasks(rnp) || rnp->qsmaskinit)) {
rnp->wait_blkd_tasks = false;
if (!rnp->qsmaskinit)
rcu_cleanup_dead_rnp(rnp);
}
raw_spin_unlock_irq_rcu_node(rnp);
raw_spin_unlock(&rcu_state.ofl_lock);
}
rcu_gp_slow(gp_preinit_delay); /* Races with CPU hotplug. */
/*
* Set the quiescent-state-needed bits in all the rcu_node
* structures for all currently online CPUs in breadth-first
* order, starting from the root rcu_node structure, relying on the
* layout of the tree within the rcu_state.node[] array. Note that
* other CPUs will access only the leaves of the hierarchy, thus
* seeing that no grace period is in progress, at least until the
* corresponding leaf node has been initialized.
*
* The grace period cannot complete until the initialization
* process finishes, because this kthread handles both.
*/
rcu_state.gp_state = RCU_GP_INIT;
rcu_for_each_node_breadth_first(rnp) {
rcu_gp_slow(gp_init_delay);
raw_spin_lock_irqsave_rcu_node(rnp, flags);
rdp = this_cpu_ptr(&rcu_data);
rcu_preempt_check_blocked_tasks(rnp);
rnp->qsmask = rnp->qsmaskinit;
WRITE_ONCE(rnp->gp_seq, rcu_state.gp_seq);
if (rnp == rdp->mynode)
(void)__note_gp_changes(rnp, rdp);
rcu_preempt_boost_start_gp(rnp);
trace_rcu_grace_period_init(rcu_state.name, rnp->gp_seq,
rnp->level, rnp->grplo,
rnp->grphi, rnp->qsmask);
/* Quiescent states for tasks on any now-offline CPUs. */
mask = rnp->qsmask & ~rnp->qsmaskinitnext;
rnp->rcu_gp_init_mask = mask;
if ((mask || rnp->wait_blkd_tasks) && rcu_is_leaf_node(rnp))
rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
else
raw_spin_unlock_irq_rcu_node(rnp);
cond_resched_tasks_rcu_qs();
WRITE_ONCE(rcu_state.gp_activity, jiffies);
}
return true;
}
/*
* Helper function for swait_event_idle_exclusive() wakeup at force-quiescent-state
* time.
*/
static bool rcu_gp_fqs_check_wake(int *gfp)
{
struct rcu_node *rnp = rcu_get_root();
/* Someone like call_rcu() requested a force-quiescent-state scan. */
*gfp = READ_ONCE(rcu_state.gp_flags);
if (*gfp & RCU_GP_FLAG_FQS)
return true;
/* The current grace period has completed. */
if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp))
return true;
return false;
}
/*
* Do one round of quiescent-state forcing.
*/
static void rcu_gp_fqs(bool first_time)
{
struct rcu_node *rnp = rcu_get_root();
WRITE_ONCE(rcu_state.gp_activity, jiffies);
rcu_state.n_force_qs++;
if (first_time) {
/* Collect dyntick-idle snapshots. */
force_qs_rnp(dyntick_save_progress_counter);
} else {
/* Handle dyntick-idle and offline CPUs. */
force_qs_rnp(rcu_implicit_dynticks_qs);
}
/* Clear flag to prevent immediate re-entry. */
if (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) {
raw_spin_lock_irq_rcu_node(rnp);
WRITE_ONCE(rcu_state.gp_flags,
READ_ONCE(rcu_state.gp_flags) & ~RCU_GP_FLAG_FQS);
raw_spin_unlock_irq_rcu_node(rnp);
}
}
/*
* Loop doing repeated quiescent-state forcing until the grace period ends.
*/
static void rcu_gp_fqs_loop(void)
{
bool first_gp_fqs;
int gf;
unsigned long j;
int ret;
struct rcu_node *rnp = rcu_get_root();
first_gp_fqs = true;
j = READ_ONCE(jiffies_till_first_fqs);
ret = 0;
for (;;) {
if (!ret) {
rcu_state.jiffies_force_qs = jiffies + j;
WRITE_ONCE(rcu_state.jiffies_kick_kthreads,
jiffies + (j ? 3 * j : 2));
}
trace_rcu_grace_period(rcu_state.name,
READ_ONCE(rcu_state.gp_seq),
TPS("fqswait"));
rcu_state.gp_state = RCU_GP_WAIT_FQS;
ret = swait_event_idle_timeout_exclusive(
rcu_state.gp_wq, rcu_gp_fqs_check_wake(&gf), j);
rcu_state.gp_state = RCU_GP_DOING_FQS;
/* Locking provides needed memory barriers. */
/* If grace period done, leave loop. */
if (!READ_ONCE(rnp->qsmask) &&
!rcu_preempt_blocked_readers_cgp(rnp))
break;
/* If time for quiescent-state forcing, do it. */
if (ULONG_CMP_GE(jiffies, rcu_state.jiffies_force_qs) ||
(gf & RCU_GP_FLAG_FQS)) {
trace_rcu_grace_period(rcu_state.name,
READ_ONCE(rcu_state.gp_seq),
TPS("fqsstart"));
rcu_gp_fqs(first_gp_fqs);
first_gp_fqs = false;
trace_rcu_grace_period(rcu_state.name,
READ_ONCE(rcu_state.gp_seq),
TPS("fqsend"));
cond_resched_tasks_rcu_qs();
WRITE_ONCE(rcu_state.gp_activity, jiffies);
ret = 0; /* Force full wait till next FQS. */
j = READ_ONCE(jiffies_till_next_fqs);
} else {
/* Deal with stray signal. */
cond_resched_tasks_rcu_qs();
WRITE_ONCE(rcu_state.gp_activity, jiffies);
WARN_ON(signal_pending(current));
trace_rcu_grace_period(rcu_state.name,
READ_ONCE(rcu_state.gp_seq),
TPS("fqswaitsig"));
ret = 1; /* Keep old FQS timing. */
j = jiffies;
if (time_after(jiffies, rcu_state.jiffies_force_qs))
j = 1;
else
j = rcu_state.jiffies_force_qs - j;
}
}
}
/*
* Clean up after the old grace period.
*/
static void rcu_gp_cleanup(void)
{
unsigned long gp_duration;
bool needgp = false;
unsigned long new_gp_seq;
bool offloaded;
struct rcu_data *rdp;
struct rcu_node *rnp = rcu_get_root();
struct swait_queue_head *sq;
WRITE_ONCE(rcu_state.gp_activity, jiffies);
raw_spin_lock_irq_rcu_node(rnp);
rcu_state.gp_end = jiffies;
gp_duration = rcu_state.gp_end - rcu_state.gp_start;
if (gp_duration > rcu_state.gp_max)
rcu_state.gp_max = gp_duration;
/*
* We know the grace period is complete, but to everyone else
* it appears to still be ongoing. But it is also the case
* that to everyone else it looks like there is nothing that
* they can do to advance the grace period. It is therefore
* safe for us to drop the lock in order to mark the grace
* period as completed in all of the rcu_node structures.
*/
raw_spin_unlock_irq_rcu_node(rnp);
/*
* Propagate new ->gp_seq value to rcu_node structures so that
* other CPUs don't have to wait until the start of the next grace
* period to process their callbacks. This also avoids some nasty
* RCU grace-period initialization races by forcing the end of
* the current grace period to be completely recorded in all of
* the rcu_node structures before the beginning of the next grace
* period is recorded in any of the rcu_node structures.
*/
new_gp_seq = rcu_state.gp_seq;
rcu_seq_end(&new_gp_seq);
rcu_for_each_node_breadth_first(rnp) {
raw_spin_lock_irq_rcu_node(rnp);
if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)))
dump_blkd_tasks(rnp, 10);
WARN_ON_ONCE(rnp->qsmask);
WRITE_ONCE(rnp->gp_seq, new_gp_seq);
rdp = this_cpu_ptr(&rcu_data);
if (rnp == rdp->mynode)
needgp = __note_gp_changes(rnp, rdp) || needgp;
/* smp_mb() provided by prior unlock-lock pair. */
needgp = rcu_future_gp_cleanup(rnp) || needgp;
sq = rcu_nocb_gp_get(rnp);
raw_spin_unlock_irq_rcu_node(rnp);
rcu_nocb_gp_cleanup(sq);
cond_resched_tasks_rcu_qs();
WRITE_ONCE(rcu_state.gp_activity, jiffies);
rcu_gp_slow(gp_cleanup_delay);
}
rnp = rcu_get_root();
raw_spin_lock_irq_rcu_node(rnp); /* GP before ->gp_seq update. */
/* Declare grace period done, trace first to use old GP number. */
trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("end"));
rcu_seq_end(&rcu_state.gp_seq);
rcu_state.gp_state = RCU_GP_IDLE;
/* Check for GP requests since above loop. */
rdp = this_cpu_ptr(&rcu_data);
if (!needgp && ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed)) {
trace_rcu_this_gp(rnp, rdp, rnp->gp_seq_needed,
TPS("CleanupMore"));
needgp = true;
}
/* Advance CBs to reduce false positives below. */
offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
rcu_segcblist_is_offloaded(&rdp->cblist);
if ((offloaded || !rcu_accelerate_cbs(rnp, rdp)) && needgp) {
WRITE_ONCE(rcu_state.gp_flags, RCU_GP_FLAG_INIT);
rcu_state.gp_req_activity = jiffies;
trace_rcu_grace_period(rcu_state.name,
READ_ONCE(rcu_state.gp_seq),
TPS("newreq"));
} else {
WRITE_ONCE(rcu_state.gp_flags,
rcu_state.gp_flags & RCU_GP_FLAG_INIT);
}
raw_spin_unlock_irq_rcu_node(rnp);
}
/*
* Body of kthread that handles grace periods.
*/
static int __noreturn rcu_gp_kthread(void *unused)
{
rcu_bind_gp_kthread();
for (;;) {
/* Handle grace-period start. */
for (;;) {
trace_rcu_grace_period(rcu_state.name,
READ_ONCE(rcu_state.gp_seq),
TPS("reqwait"));
rcu_state.gp_state = RCU_GP_WAIT_GPS;
swait_event_idle_exclusive(rcu_state.gp_wq,
READ_ONCE(rcu_state.gp_flags) &
RCU_GP_FLAG_INIT);
rcu_state.gp_state = RCU_GP_DONE_GPS;
/* Locking provides needed memory barrier. */
if (rcu_gp_init())
break;
cond_resched_tasks_rcu_qs();
WRITE_ONCE(rcu_state.gp_activity, jiffies);
WARN_ON(signal_pending(current));
trace_rcu_grace_period(rcu_state.name,
READ_ONCE(rcu_state.gp_seq),
TPS("reqwaitsig"));
}
/* Handle quiescent-state forcing. */
rcu_gp_fqs_loop();
/* Handle grace-period end. */
rcu_state.gp_state = RCU_GP_CLEANUP;
rcu_gp_cleanup();
rcu_state.gp_state = RCU_GP_CLEANED;
}
}
/*
* Report a full set of quiescent states to the rcu_state data structure.
* Invoke rcu_gp_kthread_wake() to awaken the grace-period kthread if
* another grace period is required. Whether we wake the grace-period
* kthread or it awakens itself for the next round of quiescent-state
* forcing, that kthread will clean up after the just-completed grace
* period. Note that the caller must hold rnp->lock, which is released
* before return.
*/
static void rcu_report_qs_rsp(unsigned long flags)
__releases(rcu_get_root()->lock)
{
raw_lockdep_assert_held_rcu_node(rcu_get_root());
WARN_ON_ONCE(!rcu_gp_in_progress());
WRITE_ONCE(rcu_state.gp_flags,
READ_ONCE(rcu_state.gp_flags) | RCU_GP_FLAG_FQS);
raw_spin_unlock_irqrestore_rcu_node(rcu_get_root(), flags);
rcu_gp_kthread_wake();
}
/*
* Similar to rcu_report_qs_rdp(), for which it is a helper function.
* Allows quiescent states for a group of CPUs to be reported at one go
* to the specified rcu_node structure, though all the CPUs in the group
* must be represented by the same rcu_node structure (which need not be a
* leaf rcu_node structure, though it often will be). The gps parameter
* is the grace-period snapshot, which means that the quiescent states
* are valid only if rnp->gp_seq is equal to gps. That structure's lock
* must be held upon entry, and it is released before return.
*
* As a special case, if mask is zero, the bit-already-cleared check is
* disabled. This allows propagating quiescent state due to resumed tasks
* during grace-period initialization.
*/
static void rcu_report_qs_rnp(unsigned long mask, struct rcu_node *rnp,
unsigned long gps, unsigned long flags)
__releases(rnp->lock)
{
unsigned long oldmask = 0;
struct rcu_node *rnp_c;
raw_lockdep_assert_held_rcu_node(rnp);
/* Walk up the rcu_node hierarchy. */
for (;;) {
if ((!(rnp->qsmask & mask) && mask) || rnp->gp_seq != gps) {
/*
* Our bit has already been cleared, or the
* relevant grace period is already over, so done.
*/
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
return;
}
WARN_ON_ONCE(oldmask); /* Any child must be all zeroed! */
WARN_ON_ONCE(!rcu_is_leaf_node(rnp) &&
rcu_preempt_blocked_readers_cgp(rnp));
rnp->qsmask &= ~mask;
trace_rcu_quiescent_state_report(rcu_state.name, rnp->gp_seq,
mask, rnp->qsmask, rnp->level,
rnp->grplo, rnp->grphi,
!!rnp->gp_tasks);
if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
/* Other bits still set at this level, so done. */
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
return;
}
rnp->completedqs = rnp->gp_seq;
mask = rnp->grpmask;
if (rnp->parent == NULL) {
/* No more levels. Exit loop holding root lock. */
break;
}
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
rnp_c = rnp;
rnp = rnp->parent;
raw_spin_lock_irqsave_rcu_node(rnp, flags);
oldmask = rnp_c->qsmask;
}
/*
* Get here if we are the last CPU to pass through a quiescent
* state for this grace period. Invoke rcu_report_qs_rsp()
* to clean up and start the next grace period if one is needed.
*/
rcu_report_qs_rsp(flags); /* releases rnp->lock. */
}
/*
* Record a quiescent state for all tasks that were previously queued
* on the specified rcu_node structure and that were blocking the current
* RCU grace period. The caller must hold the corresponding rnp->lock with
* irqs disabled, and this lock is released upon return, but irqs remain
* disabled.
*/
static void __maybe_unused
rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
__releases(rnp->lock)
{
unsigned long gps;
unsigned long mask;
struct rcu_node *rnp_p;
raw_lockdep_assert_held_rcu_node(rnp);
if (WARN_ON_ONCE(!IS_ENABLED(CONFIG_PREEMPT)) ||
WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)) ||
rnp->qsmask != 0) {
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
return; /* Still need more quiescent states! */
}
rnp->completedqs = rnp->gp_seq;
rnp_p = rnp->parent;
if (rnp_p == NULL) {
/*
* Only one rcu_node structure in the tree, so don't
* try to report up to its nonexistent parent!
*/
rcu_report_qs_rsp(flags);
return;
}
/* Report up the rest of the hierarchy, tracking current ->gp_seq. */
gps = rnp->gp_seq;
mask = rnp->grpmask;
raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
raw_spin_lock_rcu_node(rnp_p); /* irqs already disabled. */
rcu_report_qs_rnp(mask, rnp_p, gps, flags);
}
/*
* Record a quiescent state for the specified CPU to that CPU's rcu_data
* structure. This must be called from the specified CPU.
*/
static void
rcu_report_qs_rdp(int cpu, struct rcu_data *rdp)
{
unsigned long flags;
unsigned long mask;
bool needwake = false;
const bool offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
rcu_segcblist_is_offloaded(&rdp->cblist);
struct rcu_node *rnp;
rnp = rdp->mynode;
raw_spin_lock_irqsave_rcu_node(rnp, flags);
if (rdp->cpu_no_qs.b.norm || rdp->gp_seq != rnp->gp_seq ||
rdp->gpwrap) {
/*
* The grace period in which this quiescent state was
* recorded has ended, so don't report it upwards.
* We will instead need a new quiescent state that lies
* within the current grace period.
*/
rdp->cpu_no_qs.b.norm = true; /* need qs for new gp. */
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
return;
}
mask = rdp->grpmask;
rdp->core_needs_qs = false;
if ((rnp->qsmask & mask) == 0) {
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
} else {
/*
* This GP can't end until cpu checks in, so all of our
* callbacks can be processed during the next GP.
*/
if (!offloaded)
needwake = rcu_accelerate_cbs(rnp, rdp);
rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
/* ^^^ Released rnp->lock */
if (needwake)
rcu_gp_kthread_wake();
}
}
/*
* Check to see if there is a new grace period of which this CPU
* is not yet aware, and if so, set up local rcu_data state for it.
* Otherwise, see if this CPU has just passed through its first
* quiescent state for this grace period, and record that fact if so.
*/
static void
rcu_check_quiescent_state(struct rcu_data *rdp)
{
/* Check for grace-period ends and beginnings. */
note_gp_changes(rdp);
/*
* Does this CPU still need to do its part for current grace period?
* If no, return and let the other CPUs do their part as well.
*/
if (!rdp->core_needs_qs)
return;
/*
* Was there a quiescent state since the beginning of the grace
* period? If no, then exit and wait for the next call.
*/
if (rdp->cpu_no_qs.b.norm)
return;
/*
* Tell RCU we are done (but rcu_report_qs_rdp() will be the
* judge of that).
*/
rcu_report_qs_rdp(rdp->cpu, rdp);
}
/*
* Near the end of the offline process. Trace the fact that this CPU
* is going offline.
*/
int rcutree_dying_cpu(unsigned int cpu)
{
bool blkd;
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
struct rcu_node *rnp = rdp->mynode;
if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
return 0;
blkd = !!(rnp->qsmask & rdp->grpmask);
trace_rcu_grace_period(rcu_state.name, rnp->gp_seq,
blkd ? TPS("cpuofl") : TPS("cpuofl-bgp"));
return 0;
}
/*
* All CPUs for the specified rcu_node structure have gone offline,
* and all tasks that were preempted within an RCU read-side critical
* section while running on one of those CPUs have since exited their RCU
* read-side critical section. Some other CPU is reporting this fact with
* the specified rcu_node structure's ->lock held and interrupts disabled.
* This function therefore goes up the tree of rcu_node structures,
* clearing the corresponding bits in the ->qsmaskinit fields. Note that
* the leaf rcu_node structure's ->qsmaskinit field has already been
* updated.
*
* This function does check that the specified rcu_node structure has
* all CPUs offline and no blocked tasks, so it is OK to invoke it
* prematurely. That said, invoking it after the fact will cost you
* a needless lock acquisition. So once it has done its work, don't
* invoke it again.
*/
static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf)
{
long mask;
struct rcu_node *rnp = rnp_leaf;
raw_lockdep_assert_held_rcu_node(rnp_leaf);
if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) ||
WARN_ON_ONCE(rnp_leaf->qsmaskinit) ||
WARN_ON_ONCE(rcu_preempt_has_tasks(rnp_leaf)))
return;
for (;;) {
mask = rnp->grpmask;
rnp = rnp->parent;
if (!rnp)
break;
raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
rnp->qsmaskinit &= ~mask;
/* Between grace periods, so better already be zero! */
WARN_ON_ONCE(rnp->qsmask);
if (rnp->qsmaskinit) {
raw_spin_unlock_rcu_node(rnp);
/* irqs remain disabled. */
return;
}
raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
}
}
/*
* The CPU has been completely removed, and some other CPU is reporting
* this fact from process context. Do the remainder of the cleanup.
* There can only be one CPU hotplug operation at a time, so no need for
* explicit locking.
*/
int rcutree_dead_cpu(unsigned int cpu)
{
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
return 0;
/* Adjust any no-longer-needed kthreads. */
rcu_boost_kthread_setaffinity(rnp, -1);
/* Do any needed no-CB deferred wakeups from this CPU. */
do_nocb_deferred_wakeup(per_cpu_ptr(&rcu_data, cpu));
return 0;
}
/*
* Invoke any RCU callbacks that have made it to the end of their grace
* period. Thottle as specified by rdp->blimit.
*/
static void rcu_do_batch(struct rcu_data *rdp)
{
unsigned long flags;
const bool offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
rcu_segcblist_is_offloaded(&rdp->cblist);
struct rcu_head *rhp;
struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl);
long bl, count;
long pending, tlimit = 0;
/* If no callbacks are ready, just return. */
if (!rcu_segcblist_ready_cbs(&rdp->cblist)) {
trace_rcu_batch_start(rcu_state.name,
rcu_segcblist_n_lazy_cbs(&rdp->cblist),
rcu_segcblist_n_cbs(&rdp->cblist), 0);
trace_rcu_batch_end(rcu_state.name, 0,
!rcu_segcblist_empty(&rdp->cblist),
need_resched(), is_idle_task(current),
rcu_is_callbacks_kthread());
return;
}
/*
* Extract the list of ready callbacks, disabling to prevent
* races with call_rcu() from interrupt handlers. Leave the
* callback counts, as rcu_barrier() needs to be conservative.
*/
local_irq_save(flags);
rcu_nocb_lock(rdp);
WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
pending = rcu_segcblist_n_cbs(&rdp->cblist);
bl = max(rdp->blimit, pending >> rcu_divisor);
if (unlikely(bl > 100))
tlimit = local_clock() + rcu_resched_ns;
trace_rcu_batch_start(rcu_state.name,
rcu_segcblist_n_lazy_cbs(&rdp->cblist),
rcu_segcblist_n_cbs(&rdp->cblist), bl);
rcu_segcblist_extract_done_cbs(&rdp->cblist, &rcl);
if (offloaded)
rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);
rcu_nocb_unlock_irqrestore(rdp, flags);
/* Invoke callbacks. */
rhp = rcu_cblist_dequeue(&rcl);
for (; rhp; rhp = rcu_cblist_dequeue(&rcl)) {
debug_rcu_head_unqueue(rhp);
if (__rcu_reclaim(rcu_state.name, rhp))
rcu_cblist_dequeued_lazy(&rcl);
/*
* Stop only if limit reached and CPU has something to do.
* Note: The rcl structure counts down from zero.
*/
if (-rcl.len >= bl && !offloaded &&
(need_resched() ||
(!is_idle_task(current) && !rcu_is_callbacks_kthread())))
break;
if (unlikely(tlimit)) {
/* only call local_clock() every 32 callbacks */
if (likely((-rcl.len & 31) || local_clock() < tlimit))
continue;
/* Exceeded the time limit, so leave. */
break;
}
if (offloaded) {
WARN_ON_ONCE(in_serving_softirq());
local_bh_enable();
lockdep_assert_irqs_enabled();
cond_resched_tasks_rcu_qs();
lockdep_assert_irqs_enabled();
local_bh_disable();
}
}
local_irq_save(flags);
rcu_nocb_lock(rdp);
count = -rcl.len;
trace_rcu_batch_end(rcu_state.name, count, !!rcl.head, need_resched(),
is_idle_task(current), rcu_is_callbacks_kthread());
/* Update counts and requeue any remaining callbacks. */
rcu_segcblist_insert_done_cbs(&rdp->cblist, &rcl);
smp_mb(); /* List handling before counting for rcu_barrier(). */
rcu_segcblist_insert_count(&rdp->cblist, &rcl);
/* Reinstate batch limit if we have worked down the excess. */
count = rcu_segcblist_n_cbs(&rdp->cblist);
if (rdp->blimit >= DEFAULT_MAX_RCU_BLIMIT && count <= qlowmark)
rdp->blimit = blimit;
/* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
if (count == 0 && rdp->qlen_last_fqs_check != 0) {
rdp->qlen_last_fqs_check = 0;
rdp->n_force_qs_snap = rcu_state.n_force_qs;
} else if (count < rdp->qlen_last_fqs_check - qhimark)
rdp->qlen_last_fqs_check = count;
/*
* The following usually indicates a double call_rcu(). To track
* this down, try building with CONFIG_DEBUG_OBJECTS_RCU_HEAD=y.
*/
WARN_ON_ONCE(count == 0 && !rcu_segcblist_empty(&rdp->cblist));
WARN_ON_ONCE(!IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
count != 0 && rcu_segcblist_empty(&rdp->cblist));
rcu_nocb_unlock_irqrestore(rdp, flags);
/* Re-invoke RCU core processing if there are callbacks remaining. */
if (!offloaded && rcu_segcblist_ready_cbs(&rdp->cblist))
invoke_rcu_core();
}
/*
* This function is invoked from each scheduling-clock interrupt,
* and checks to see if this CPU is in a non-context-switch quiescent
* state, for example, user mode or idle loop. It also schedules RCU
* core processing. If the current grace period has gone on too long,
* it will ask the scheduler to manufacture a context switch for the sole
* purpose of providing a providing the needed quiescent state.
*/
void rcu_sched_clock_irq(int user)
{
trace_rcu_utilization(TPS("Start scheduler-tick"));
raw_cpu_inc(rcu_data.ticks_this_gp);
/* The load-acquire pairs with the store-release setting to true. */
if (smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs))) {
/* Idle and userspace execution already are quiescent states. */
if (!rcu_is_cpu_rrupt_from_idle() && !user) {
set_tsk_need_resched(current);
set_preempt_need_resched();
}
__this_cpu_write(rcu_data.rcu_urgent_qs, false);
}
rcu_flavor_sched_clock_irq(user);
if (rcu_pending())
invoke_rcu_core();
trace_rcu_utilization(TPS("End scheduler-tick"));
}
/*
* Scan the leaf rcu_node structures. For each structure on which all
* CPUs have reported a quiescent state and on which there are tasks
* blocking the current grace period, initiate RCU priority boosting.
* Otherwise, invoke the specified function to check dyntick state for
* each CPU that has not yet reported a quiescent state.
*/
static void force_qs_rnp(int (*f)(struct rcu_data *rdp))
{
int cpu;
unsigned long flags;
unsigned long mask;
struct rcu_node *rnp;
rcu_for_each_leaf_node(rnp) {
cond_resched_tasks_rcu_qs();
mask = 0;
raw_spin_lock_irqsave_rcu_node(rnp, flags);
if (rnp->qsmask == 0) {
if (!IS_ENABLED(CONFIG_PREEMPT) ||
rcu_preempt_blocked_readers_cgp(rnp)) {
/*
* No point in scanning bits because they
* are all zero. But we might need to
* priority-boost blocked readers.
*/
rcu_initiate_boost(rnp, flags);
/* rcu_initiate_boost() releases rnp->lock */
continue;
}
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
continue;
}
for_each_leaf_node_possible_cpu(rnp, cpu) {
unsigned long bit = leaf_node_cpu_bit(rnp, cpu);
if ((rnp->qsmask & bit) != 0) {
if (f(per_cpu_ptr(&rcu_data, cpu)))
mask |= bit;
}
}
if (mask != 0) {
/* Idle/offline CPUs, report (releases rnp->lock). */
rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
} else {
/* Nothing to do here, so just drop the lock. */
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
}
}
/*
* Force quiescent states on reluctant CPUs, and also detect which
* CPUs are in dyntick-idle mode.
*/
void rcu_force_quiescent_state(void)
{
unsigned long flags;
bool ret;
struct rcu_node *rnp;
struct rcu_node *rnp_old = NULL;
/* Funnel through hierarchy to reduce memory contention. */
rnp = __this_cpu_read(rcu_data.mynode);
for (; rnp != NULL; rnp = rnp->parent) {
ret = (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) ||
!raw_spin_trylock(&rnp->fqslock);
if (rnp_old != NULL)
raw_spin_unlock(&rnp_old->fqslock);
if (ret)
return;
rnp_old = rnp;
}
/* rnp_old == rcu_get_root(), rnp == NULL. */
/* Reached the root of the rcu_node tree, acquire lock. */
raw_spin_lock_irqsave_rcu_node(rnp_old, flags);
raw_spin_unlock(&rnp_old->fqslock);
if (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) {
raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
return; /* Someone beat us to it. */
}
WRITE_ONCE(rcu_state.gp_flags,
READ_ONCE(rcu_state.gp_flags) | RCU_GP_FLAG_FQS);
raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
rcu_gp_kthread_wake();
}
EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
/* Perform RCU core processing work for the current CPU. */
static __latent_entropy void rcu_core(void)
{
unsigned long flags;
struct rcu_data *rdp = raw_cpu_ptr(&rcu_data);
struct rcu_node *rnp = rdp->mynode;
const bool offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
rcu_segcblist_is_offloaded(&rdp->cblist);
if (cpu_is_offline(smp_processor_id()))
return;
trace_rcu_utilization(TPS("Start RCU core"));
WARN_ON_ONCE(!rdp->beenonline);
/* Report any deferred quiescent states if preemption enabled. */
if (!(preempt_count() & PREEMPT_MASK)) {
rcu_preempt_deferred_qs(current);
} else if (rcu_preempt_need_deferred_qs(current)) {
set_tsk_need_resched(current);
set_preempt_need_resched();
}
/* Update RCU state based on any recent quiescent states. */
rcu_check_quiescent_state(rdp);
/* No grace period and unregistered callbacks? */
if (!rcu_gp_in_progress() &&
rcu_segcblist_is_enabled(&rdp->cblist) && !offloaded) {
local_irq_save(flags);
if (!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
rcu_accelerate_cbs_unlocked(rnp, rdp);
local_irq_restore(flags);
}
rcu_check_gp_start_stall(rnp, rdp, rcu_jiffies_till_stall_check());
/* If there are callbacks ready, invoke them. */
if (!offloaded && rcu_segcblist_ready_cbs(&rdp->cblist) &&
likely(READ_ONCE(rcu_scheduler_fully_active)))
rcu_do_batch(rdp);
/* Do any needed deferred wakeups of rcuo kthreads. */
do_nocb_deferred_wakeup(rdp);
trace_rcu_utilization(TPS("End RCU core"));
}
static void rcu_core_si(struct softirq_action *h)
{
rcu_core();
}
static void rcu_wake_cond(struct task_struct *t, int status)
{
/*
* If the thread is yielding, only wake it when this
* is invoked from idle
*/
if (t && (status != RCU_KTHREAD_YIELDING || is_idle_task(current)))
wake_up_process(t);
}
static void invoke_rcu_core_kthread(void)
{
struct task_struct *t;
unsigned long flags;
local_irq_save(flags);
__this_cpu_write(rcu_data.rcu_cpu_has_work, 1);
t = __this_cpu_read(rcu_data.rcu_cpu_kthread_task);
if (t != NULL && t != current)
rcu_wake_cond(t, __this_cpu_read(rcu_data.rcu_cpu_kthread_status));
local_irq_restore(flags);
}
/*
* Wake up this CPU's rcuc kthread to do RCU core processing.
*/
static void invoke_rcu_core(void)
{
if (!cpu_online(smp_processor_id()))
return;
if (use_softirq)
raise_softirq(RCU_SOFTIRQ);
else
invoke_rcu_core_kthread();
}
static void rcu_cpu_kthread_park(unsigned int cpu)
{
per_cpu(rcu_data.rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
}
static int rcu_cpu_kthread_should_run(unsigned int cpu)
{
return __this_cpu_read(rcu_data.rcu_cpu_has_work);
}
/*
* Per-CPU kernel thread that invokes RCU callbacks. This replaces
* the RCU softirq used in configurations of RCU that do not support RCU
* priority boosting.
*/
static void rcu_cpu_kthread(unsigned int cpu)
{
unsigned int *statusp = this_cpu_ptr(&rcu_data.rcu_cpu_kthread_status);
char work, *workp = this_cpu_ptr(&rcu_data.rcu_cpu_has_work);
int spincnt;
for (spincnt = 0; spincnt < 10; spincnt++) {
trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait"));
local_bh_disable();
*statusp = RCU_KTHREAD_RUNNING;
local_irq_disable();
work = *workp;
*workp = 0;
local_irq_enable();
if (work)
rcu_core();
local_bh_enable();
if (*workp == 0) {
trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
*statusp = RCU_KTHREAD_WAITING;
return;
}
}
*statusp = RCU_KTHREAD_YIELDING;
trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
schedule_timeout_interruptible(2);
trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
*statusp = RCU_KTHREAD_WAITING;
}
static struct smp_hotplug_thread rcu_cpu_thread_spec = {
.store = &rcu_data.rcu_cpu_kthread_task,
.thread_should_run = rcu_cpu_kthread_should_run,
.thread_fn = rcu_cpu_kthread,
.thread_comm = "rcuc/%u",
.setup = rcu_cpu_kthread_setup,
.park = rcu_cpu_kthread_park,
};
/*
* Spawn per-CPU RCU core processing kthreads.
*/
static int __init rcu_spawn_core_kthreads(void)
{
int cpu;
for_each_possible_cpu(cpu)
per_cpu(rcu_data.rcu_cpu_has_work, cpu) = 0;
if (!IS_ENABLED(CONFIG_RCU_BOOST) && use_softirq)
return 0;
WARN_ONCE(smpboot_register_percpu_thread(&rcu_cpu_thread_spec),
"%s: Could not start rcuc kthread, OOM is now expected behavior\n", __func__);
return 0;
}
early_initcall(rcu_spawn_core_kthreads);
/*
* Handle any core-RCU processing required by a call_rcu() invocation.
*/
static void __call_rcu_core(struct rcu_data *rdp, struct rcu_head *head,
unsigned long flags)
{
/*
* If called from an extended quiescent state, invoke the RCU
* core in order to force a re-evaluation of RCU's idleness.
*/
if (!rcu_is_watching())
invoke_rcu_core();
/* If interrupts were disabled or CPU offline, don't invoke RCU core. */
if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
return;
/*
* Force the grace period if too many callbacks or too long waiting.
* Enforce hysteresis, and don't invoke rcu_force_quiescent_state()
* if some other CPU has recently done so. Also, don't bother
* invoking rcu_force_quiescent_state() if the newly enqueued callback
* is the only one waiting for a grace period to complete.
*/
if (unlikely(rcu_segcblist_n_cbs(&rdp->cblist) >
rdp->qlen_last_fqs_check + qhimark)) {
/* Are we ignoring a completed grace period? */
note_gp_changes(rdp);
/* Start a new grace period if one not already started. */
if (!rcu_gp_in_progress()) {
rcu_accelerate_cbs_unlocked(rdp->mynode, rdp);
} else {
/* Give the grace period a kick. */
rdp->blimit = DEFAULT_MAX_RCU_BLIMIT;
if (rcu_state.n_force_qs == rdp->n_force_qs_snap &&
rcu_segcblist_first_pend_cb(&rdp->cblist) != head)
rcu_force_quiescent_state();
rdp->n_force_qs_snap = rcu_state.n_force_qs;
rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);
}
}
}
/*
* RCU callback function to leak a callback.
*/
static void rcu_leak_callback(struct rcu_head *rhp)
{
}
/*
* Helper function for call_rcu() and friends. The cpu argument will
* normally be -1, indicating "currently running CPU". It may specify
* a CPU only if that CPU is a no-CBs CPU. Currently, only rcu_barrier()
* is expected to specify a CPU.
*/
static void
__call_rcu(struct rcu_head *head, rcu_callback_t func, bool lazy)
{
unsigned long flags;
struct rcu_data *rdp;
bool was_alldone;
/* Misaligned rcu_head! */
WARN_ON_ONCE((unsigned long)head & (sizeof(void *) - 1));
if (debug_rcu_head_queue(head)) {
/*
* Probable double call_rcu(), so leak the callback.
* Use rcu:rcu_callback trace event to find the previous
* time callback was passed to __call_rcu().
*/
WARN_ONCE(1, "__call_rcu(): Double-freed CB %p->%pS()!!!\n",
head, head->func);
WRITE_ONCE(head->func, rcu_leak_callback);
return;
}
head->func = func;
head->next = NULL;
local_irq_save(flags);
rdp = this_cpu_ptr(&rcu_data);
/* Add the callback to our list. */
if (unlikely(!rcu_segcblist_is_enabled(&rdp->cblist))) {
// This can trigger due to call_rcu() from offline CPU:
WARN_ON_ONCE(rcu_scheduler_active != RCU_SCHEDULER_INACTIVE);
WARN_ON_ONCE(!rcu_is_watching());
// Very early boot, before rcu_init(). Initialize if needed
// and then drop through to queue the callback.
if (rcu_segcblist_empty(&rdp->cblist))
rcu_segcblist_init(&rdp->cblist);
}
if (rcu_nocb_try_bypass(rdp, head, &was_alldone, flags))
return; // Enqueued onto ->nocb_bypass, so just leave.
/* If we get here, rcu_nocb_try_bypass() acquired ->nocb_lock. */
rcu_segcblist_enqueue(&rdp->cblist, head, lazy);
if (__is_kfree_rcu_offset((unsigned long)func))
trace_rcu_kfree_callback(rcu_state.name, head,
(unsigned long)func,
rcu_segcblist_n_lazy_cbs(&rdp->cblist),
rcu_segcblist_n_cbs(&rdp->cblist));
else
trace_rcu_callback(rcu_state.name, head,
rcu_segcblist_n_lazy_cbs(&rdp->cblist),
rcu_segcblist_n_cbs(&rdp->cblist));
/* Go handle any RCU core processing required. */
if (IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
unlikely(rcu_segcblist_is_offloaded(&rdp->cblist))) {
__call_rcu_nocb_wake(rdp, was_alldone, flags); /* unlocks */
} else {
__call_rcu_core(rdp, head, flags);
local_irq_restore(flags);
}
}
/**
* call_rcu() - Queue an RCU callback for invocation after a grace period.
* @head: structure to be used for queueing the RCU updates.
* @func: actual callback function to be invoked after the grace period
*
* The callback function will be invoked some time after a full grace
* period elapses, in other words after all pre-existing RCU read-side
* critical sections have completed. However, the callback function
* might well execute concurrently with RCU read-side critical sections
* that started after call_rcu() was invoked. RCU read-side critical
* sections are delimited by rcu_read_lock() and rcu_read_unlock(), and
* may be nested. In addition, regions of code across which interrupts,
* preemption, or softirqs have been disabled also serve as RCU read-side
* critical sections. This includes hardware interrupt handlers, softirq
* handlers, and NMI handlers.
*
* Note that all CPUs must agree that the grace period extended beyond
* all pre-existing RCU read-side critical section. On systems with more
* than one CPU, this means that when "func()" is invoked, each CPU is
* guaranteed to have executed a full memory barrier since the end of its
* last RCU read-side critical section whose beginning preceded the call
* to call_rcu(). It also means that each CPU executing an RCU read-side
* critical section that continues beyond the start of "func()" must have
* executed a memory barrier after the call_rcu() but before the beginning
* of that RCU read-side critical section. Note that these guarantees
* include CPUs that are offline, idle, or executing in user mode, as
* well as CPUs that are executing in the kernel.
*
* Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
* resulting RCU callback function "func()", then both CPU A and CPU B are
* guaranteed to execute a full memory barrier during the time interval
* between the call to call_rcu() and the invocation of "func()" -- even
* if CPU A and CPU B are the same CPU (but again only if the system has
* more than one CPU).
*/
void call_rcu(struct rcu_head *head, rcu_callback_t func)
{
__call_rcu(head, func, 0);
}
EXPORT_SYMBOL_GPL(call_rcu);
/*
* Queue an RCU callback for lazy invocation after a grace period.
* This will likely be later named something like "call_rcu_lazy()",
* but this change will require some way of tagging the lazy RCU
* callbacks in the list of pending callbacks. Until then, this
* function may only be called from __kfree_rcu().
*/
void kfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
{
__call_rcu(head, func, 1);
}
EXPORT_SYMBOL_GPL(kfree_call_rcu);
/*
* During early boot, any blocking grace-period wait automatically
* implies a grace period. Later on, this is never the case for PREEMPT.
*
* Howevr, because a context switch is a grace period for !PREEMPT, any
* blocking grace-period wait automatically implies a grace period if
* there is only one CPU online at any point time during execution of
* either synchronize_rcu() or synchronize_rcu_expedited(). It is OK to
* occasionally incorrectly indicate that there are multiple CPUs online
* when there was in fact only one the whole time, as this just adds some
* overhead: RCU still operates correctly.
*/
static int rcu_blocking_is_gp(void)
{
int ret;
if (IS_ENABLED(CONFIG_PREEMPT))
return rcu_scheduler_active == RCU_SCHEDULER_INACTIVE;
might_sleep(); /* Check for RCU read-side critical section. */
preempt_disable();
ret = num_online_cpus() <= 1;
preempt_enable();
return ret;
}
/**
* synchronize_rcu - wait until a grace period has elapsed.
*
* Control will return to the caller some time after a full grace
* period has elapsed, in other words after all currently executing RCU
* read-side critical sections have completed. Note, however, that
* upon return from synchronize_rcu(), the caller might well be executing
* concurrently with new RCU read-side critical sections that began while
* synchronize_rcu() was waiting. RCU read-side critical sections are
* delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
* In addition, regions of code across which interrupts, preemption, or
* softirqs have been disabled also serve as RCU read-side critical
* sections. This includes hardware interrupt handlers, softirq handlers,
* and NMI handlers.
*
* Note that this guarantee implies further memory-ordering guarantees.
* On systems with more than one CPU, when synchronize_rcu() returns,
* each CPU is guaranteed to have executed a full memory barrier since
* the end of its last RCU read-side critical section whose beginning
* preceded the call to synchronize_rcu(). In addition, each CPU having
* an RCU read-side critical section that extends beyond the return from
* synchronize_rcu() is guaranteed to have executed a full memory barrier
* after the beginning of synchronize_rcu() and before the beginning of
* that RCU read-side critical section. Note that these guarantees include
* CPUs that are offline, idle, or executing in user mode, as well as CPUs
* that are executing in the kernel.
*
* Furthermore, if CPU A invoked synchronize_rcu(), which returned
* to its caller on CPU B, then both CPU A and CPU B are guaranteed
* to have executed a full memory barrier during the execution of
* synchronize_rcu() -- even if CPU A and CPU B are the same CPU (but
* again only if the system has more than one CPU).
*/
void synchronize_rcu(void)
{
RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
lock_is_held(&rcu_lock_map) ||
lock_is_held(&rcu_sched_lock_map),
"Illegal synchronize_rcu() in RCU read-side critical section");
if (rcu_blocking_is_gp())
return;
if (rcu_gp_is_expedited())
synchronize_rcu_expedited();
else
wait_rcu_gp(call_rcu);
}
EXPORT_SYMBOL_GPL(synchronize_rcu);
/**
* get_state_synchronize_rcu - Snapshot current RCU state
*
* Returns a cookie that is used by a later call to cond_synchronize_rcu()
* to determine whether or not a full grace period has elapsed in the
* meantime.
*/
unsigned long get_state_synchronize_rcu(void)
{
/*
* Any prior manipulation of RCU-protected data must happen
* before the load from ->gp_seq.
*/
smp_mb(); /* ^^^ */
return rcu_seq_snap(&rcu_state.gp_seq);
}
EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);
/**
* cond_synchronize_rcu - Conditionally wait for an RCU grace period
*
* @oldstate: return value from earlier call to get_state_synchronize_rcu()
*
* If a full RCU grace period has elapsed since the earlier call to
* get_state_synchronize_rcu(), just return. Otherwise, invoke
* synchronize_rcu() to wait for a full grace period.
*
* Yes, this function does not take counter wrap into account. But
* counter wrap is harmless. If the counter wraps, we have waited for
* more than 2 billion grace periods (and way more on a 64-bit system!),
* so waiting for one additional grace period should be just fine.
*/
void cond_synchronize_rcu(unsigned long oldstate)
{
if (!rcu_seq_done(&rcu_state.gp_seq, oldstate))
synchronize_rcu();
else
smp_mb(); /* Ensure GP ends before subsequent accesses. */
}
EXPORT_SYMBOL_GPL(cond_synchronize_rcu);
/*
* Check to see if there is any immediate RCU-related work to be done by
* the current CPU, returning 1 if so and zero otherwise. The checks are
* in order of increasing expense: checks that can be carried out against
* CPU-local state are performed first. However, we must check for CPU
* stalls first, else we might not get a chance.
*/
static int rcu_pending(void)
{
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
struct rcu_node *rnp = rdp->mynode;
/* Check for CPU stalls, if enabled. */
check_cpu_stall(rdp);
/* Does this CPU need a deferred NOCB wakeup? */
if (rcu_nocb_need_deferred_wakeup(rdp))
return 1;
/* Is this CPU a NO_HZ_FULL CPU that should ignore RCU? */
if (rcu_nohz_full_cpu())
return 0;
/* Is the RCU core waiting for a quiescent state from this CPU? */
if (rdp->core_needs_qs && !rdp->cpu_no_qs.b.norm)
return 1;
/* Does this CPU have callbacks ready to invoke? */
if (rcu_segcblist_ready_cbs(&rdp->cblist))
return 1;
/* Has RCU gone idle with this CPU needing another grace period? */
if (!rcu_gp_in_progress() &&
rcu_segcblist_is_enabled(&rdp->cblist) &&
(!IS_ENABLED(CONFIG_RCU_NOCB_CPU) ||
!rcu_segcblist_is_offloaded(&rdp->cblist)) &&
!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
return 1;
/* Have RCU grace period completed or started? */
if (rcu_seq_current(&rnp->gp_seq) != rdp->gp_seq ||
unlikely(READ_ONCE(rdp->gpwrap))) /* outside lock */
return 1;
/* nothing to do */
return 0;
}
/*
* Helper function for rcu_barrier() tracing. If tracing is disabled,
* the compiler is expected to optimize this away.
*/
static void rcu_barrier_trace(const char *s, int cpu, unsigned long done)
{
trace_rcu_barrier(rcu_state.name, s, cpu,
atomic_read(&rcu_state.barrier_cpu_count), done);
}
/*
* RCU callback function for rcu_barrier(). If we are last, wake
* up the task executing rcu_barrier().
*/
static void rcu_barrier_callback(struct rcu_head *rhp)
{
if (atomic_dec_and_test(&rcu_state.barrier_cpu_count)) {
rcu_barrier_trace(TPS("LastCB"), -1,
rcu_state.barrier_sequence);
complete(&rcu_state.barrier_completion);
} else {
rcu_barrier_trace(TPS("CB"), -1, rcu_state.barrier_sequence);
}
}
/*
* Called with preemption disabled, and from cross-cpu IRQ context.
*/
static void rcu_barrier_func(void *unused)
{
struct rcu_data *rdp = raw_cpu_ptr(&rcu_data);
rcu_barrier_trace(TPS("IRQ"), -1, rcu_state.barrier_sequence);
rdp->barrier_head.func = rcu_barrier_callback;
debug_rcu_head_queue(&rdp->barrier_head);
rcu_nocb_lock(rdp);
WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies));
if (rcu_segcblist_entrain(&rdp->cblist, &rdp->barrier_head, 0)) {
atomic_inc(&rcu_state.barrier_cpu_count);
} else {
debug_rcu_head_unqueue(&rdp->barrier_head);
rcu_barrier_trace(TPS("IRQNQ"), -1,
rcu_state.barrier_sequence);
}
rcu_nocb_unlock(rdp);
}
/**
* rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
*
* Note that this primitive does not necessarily wait for an RCU grace period
* to complete. For example, if there are no RCU callbacks queued anywhere
* in the system, then rcu_barrier() is within its rights to return
* immediately, without waiting for anything, much less an RCU grace period.
*/
void rcu_barrier(void)
{
int cpu;
struct rcu_data *rdp;
unsigned long s = rcu_seq_snap(&rcu_state.barrier_sequence);
rcu_barrier_trace(TPS("Begin"), -1, s);
/* Take mutex to serialize concurrent rcu_barrier() requests. */
mutex_lock(&rcu_state.barrier_mutex);
/* Did someone else do our work for us? */
if (rcu_seq_done(&rcu_state.barrier_sequence, s)) {
rcu_barrier_trace(TPS("EarlyExit"), -1,
rcu_state.barrier_sequence);
smp_mb(); /* caller's subsequent code after above check. */
mutex_unlock(&rcu_state.barrier_mutex);
return;
}
/* Mark the start of the barrier operation. */
rcu_seq_start(&rcu_state.barrier_sequence);
rcu_barrier_trace(TPS("Inc1"), -1, rcu_state.barrier_sequence);
/*
* Initialize the count to one rather than to zero in order to
* avoid a too-soon return to zero in case of a short grace period
* (or preemption of this task). Exclude CPU-hotplug operations
* to ensure that no offline CPU has callbacks queued.
*/
init_completion(&rcu_state.barrier_completion);
atomic_set(&rcu_state.barrier_cpu_count, 1);
get_online_cpus();
/*
* Force each CPU with callbacks to register a new callback.
* When that callback is invoked, we will know that all of the
* corresponding CPU's preceding callbacks have been invoked.
*/
for_each_possible_cpu(cpu) {
rdp = per_cpu_ptr(&rcu_data, cpu);
if (!cpu_online(cpu) &&
!rcu_segcblist_is_offloaded(&rdp->cblist))
continue;
if (rcu_segcblist_n_cbs(&rdp->cblist)) {
rcu_barrier_trace(TPS("OnlineQ"), cpu,
rcu_state.barrier_sequence);
smp_call_function_single(cpu, rcu_barrier_func, NULL, 1);
} else {
rcu_barrier_trace(TPS("OnlineNQ"), cpu,
rcu_state.barrier_sequence);
}
}
put_online_cpus();
/*
* Now that we have an rcu_barrier_callback() callback on each
* CPU, and thus each counted, remove the initial count.
*/
if (atomic_dec_and_test(&rcu_state.barrier_cpu_count))
complete(&rcu_state.barrier_completion);
/* Wait for all rcu_barrier_callback() callbacks to be invoked. */
wait_for_completion(&rcu_state.barrier_completion);
/* Mark the end of the barrier operation. */
rcu_barrier_trace(TPS("Inc2"), -1, rcu_state.barrier_sequence);
rcu_seq_end(&rcu_state.barrier_sequence);
/* Other rcu_barrier() invocations can now safely proceed. */
mutex_unlock(&rcu_state.barrier_mutex);
}
EXPORT_SYMBOL_GPL(rcu_barrier);
/*
* Propagate ->qsinitmask bits up the rcu_node tree to account for the
* first CPU in a given leaf rcu_node structure coming online. The caller
* must hold the corresponding leaf rcu_node ->lock with interrrupts
* disabled.
*/
static void rcu_init_new_rnp(struct rcu_node *rnp_leaf)
{
long mask;
long oldmask;
struct rcu_node *rnp = rnp_leaf;
raw_lockdep_assert_held_rcu_node(rnp_leaf);
WARN_ON_ONCE(rnp->wait_blkd_tasks);
for (;;) {
mask = rnp->grpmask;
rnp = rnp->parent;
if (rnp == NULL)
return;
raw_spin_lock_rcu_node(rnp); /* Interrupts already disabled. */
oldmask = rnp->qsmaskinit;
rnp->qsmaskinit |= mask;
raw_spin_unlock_rcu_node(rnp); /* Interrupts remain disabled. */
if (oldmask)
return;
}
}
/*
* Do boot-time initialization of a CPU's per-CPU RCU data.
*/
static void __init
rcu_boot_init_percpu_data(int cpu)
{
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
/* Set up local state, ensuring consistent view of global state. */
rdp->grpmask = leaf_node_cpu_bit(rdp->mynode, cpu);
WARN_ON_ONCE(rdp->dynticks_nesting != 1);
WARN_ON_ONCE(rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp)));
rdp->rcu_ofl_gp_seq = rcu_state.gp_seq;
rdp->rcu_ofl_gp_flags = RCU_GP_CLEANED;
rdp->rcu_onl_gp_seq = rcu_state.gp_seq;
rdp->rcu_onl_gp_flags = RCU_GP_CLEANED;
rdp->cpu = cpu;
rcu_boot_init_nocb_percpu_data(rdp);
}
/*
* Invoked early in the CPU-online process, when pretty much all services
* are available. The incoming CPU is not present.
*
* Initializes a CPU's per-CPU RCU data. Note that only one online or
* offline event can be happening at a given time. Note also that we can
* accept some slop in the rsp->gp_seq access due to the fact that this
* CPU cannot possibly have any non-offloaded RCU callbacks in flight yet.
* And any offloaded callbacks are being numbered elsewhere.
*/
int rcutree_prepare_cpu(unsigned int cpu)
{
unsigned long flags;
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
struct rcu_node *rnp = rcu_get_root();
/* Set up local state, ensuring consistent view of global state. */
raw_spin_lock_irqsave_rcu_node(rnp, flags);
rdp->qlen_last_fqs_check = 0;
rdp->n_force_qs_snap = rcu_state.n_force_qs;
rdp->blimit = blimit;
if (rcu_segcblist_empty(&rdp->cblist) && /* No early-boot CBs? */
!rcu_segcblist_is_offloaded(&rdp->cblist))
rcu_segcblist_init(&rdp->cblist); /* Re-enable callbacks. */
rdp->dynticks_nesting = 1; /* CPU not up, no tearing. */
rcu_dynticks_eqs_online();
raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
/*
* Add CPU to leaf rcu_node pending-online bitmask. Any needed
* propagation up the rcu_node tree will happen at the beginning
* of the next grace period.
*/
rnp = rdp->mynode;
raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
rdp->beenonline = true; /* We have now been online. */
rdp->gp_seq = rnp->gp_seq;
rdp->gp_seq_needed = rnp->gp_seq;
rdp->cpu_no_qs.b.norm = true;
rdp->core_needs_qs = false;
rdp->rcu_iw_pending = false;
rdp->rcu_iw_gp_seq = rnp->gp_seq - 1;
trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("cpuonl"));
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
rcu_prepare_kthreads(cpu);
rcu_spawn_cpu_nocb_kthread(cpu);
return 0;
}
/*
* Update RCU priority boot kthread affinity for CPU-hotplug changes.
*/
static void rcutree_affinity_setting(unsigned int cpu, int outgoing)
{
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
rcu_boost_kthread_setaffinity(rdp->mynode, outgoing);
}
/*
* Near the end of the CPU-online process. Pretty much all services
* enabled, and the CPU is now very much alive.
*/
int rcutree_online_cpu(unsigned int cpu)
{
unsigned long flags;
struct rcu_data *rdp;
struct rcu_node *rnp;
rdp = per_cpu_ptr(&rcu_data, cpu);
rnp = rdp->mynode;
raw_spin_lock_irqsave_rcu_node(rnp, flags);
rnp->ffmask |= rdp->grpmask;
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
return 0; /* Too early in boot for scheduler work. */
sync_sched_exp_online_cleanup(cpu);
rcutree_affinity_setting(cpu, -1);
return 0;
}
/*
* Near the beginning of the process. The CPU is still very much alive
* with pretty much all services enabled.
*/
int rcutree_offline_cpu(unsigned int cpu)
{
unsigned long flags;
struct rcu_data *rdp;
struct rcu_node *rnp;
rdp = per_cpu_ptr(&rcu_data, cpu);
rnp = rdp->mynode;
raw_spin_lock_irqsave_rcu_node(rnp, flags);
rnp->ffmask &= ~rdp->grpmask;
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
rcutree_affinity_setting(cpu, cpu);
return 0;
}
static DEFINE_PER_CPU(int, rcu_cpu_started);
/*
* Mark the specified CPU as being online so that subsequent grace periods
* (both expedited and normal) will wait on it. Note that this means that
* incoming CPUs are not allowed to use RCU read-side critical sections
* until this function is called. Failing to observe this restriction
* will result in lockdep splats.
*
* Note that this function is special in that it is invoked directly
* from the incoming CPU rather than from the cpuhp_step mechanism.
* This is because this function must be invoked at a precise location.
*/
void rcu_cpu_starting(unsigned int cpu)
{
unsigned long flags;
unsigned long mask;
int nbits;
unsigned long oldmask;
struct rcu_data *rdp;
struct rcu_node *rnp;
if (per_cpu(rcu_cpu_started, cpu))
return;
per_cpu(rcu_cpu_started, cpu) = 1;
rdp = per_cpu_ptr(&rcu_data, cpu);
rnp = rdp->mynode;
mask = rdp->grpmask;
raw_spin_lock_irqsave_rcu_node(rnp, flags);
rnp->qsmaskinitnext |= mask;
oldmask = rnp->expmaskinitnext;
rnp->expmaskinitnext |= mask;
oldmask ^= rnp->expmaskinitnext;
nbits = bitmap_weight(&oldmask, BITS_PER_LONG);
/* Allow lockless access for expedited grace periods. */
smp_store_release(&rcu_state.ncpus, rcu_state.ncpus + nbits); /* ^^^ */
rcu_gpnum_ovf(rnp, rdp); /* Offline-induced counter wrap? */
rdp->rcu_onl_gp_seq = READ_ONCE(rcu_state.gp_seq);
rdp->rcu_onl_gp_flags = READ_ONCE(rcu_state.gp_flags);
if (rnp->qsmask & mask) { /* RCU waiting on incoming CPU? */
/* Report QS -after- changing ->qsmaskinitnext! */
rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
} else {
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
smp_mb(); /* Ensure RCU read-side usage follows above initialization. */
}
#ifdef CONFIG_HOTPLUG_CPU
/*
* The outgoing function has no further need of RCU, so remove it from
* the rcu_node tree's ->qsmaskinitnext bit masks.
*
* Note that this function is special in that it is invoked directly
* from the outgoing CPU rather than from the cpuhp_step mechanism.
* This is because this function must be invoked at a precise location.
*/
void rcu_report_dead(unsigned int cpu)
{
unsigned long flags;
unsigned long mask;
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
/* QS for any half-done expedited grace period. */
preempt_disable();
rcu_report_exp_rdp(this_cpu_ptr(&rcu_data));
preempt_enable();
rcu_preempt_deferred_qs(current);
/* Remove outgoing CPU from mask in the leaf rcu_node structure. */
mask = rdp->grpmask;
raw_spin_lock(&rcu_state.ofl_lock);
raw_spin_lock_irqsave_rcu_node(rnp, flags); /* Enforce GP memory-order guarantee. */
rdp->rcu_ofl_gp_seq = READ_ONCE(rcu_state.gp_seq);
rdp->rcu_ofl_gp_flags = READ_ONCE(rcu_state.gp_flags);
if (rnp->qsmask & mask) { /* RCU waiting on outgoing CPU? */
/* Report quiescent state -before- changing ->qsmaskinitnext! */
rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
raw_spin_lock_irqsave_rcu_node(rnp, flags);
}
rnp->qsmaskinitnext &= ~mask;
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
raw_spin_unlock(&rcu_state.ofl_lock);
per_cpu(rcu_cpu_started, cpu) = 0;
}
/*
* The outgoing CPU has just passed through the dying-idle state, and we
* are being invoked from the CPU that was IPIed to continue the offline
* operation. Migrate the outgoing CPU's callbacks to the current CPU.
*/
void rcutree_migrate_callbacks(int cpu)
{
unsigned long flags;
struct rcu_data *my_rdp;
struct rcu_node *my_rnp;
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
bool needwake;
if (rcu_segcblist_is_offloaded(&rdp->cblist) ||
rcu_segcblist_empty(&rdp->cblist))
return; /* No callbacks to migrate. */
local_irq_save(flags);
my_rdp = this_cpu_ptr(&rcu_data);
my_rnp = my_rdp->mynode;
rcu_nocb_lock(my_rdp); /* irqs already disabled. */
WARN_ON_ONCE(!rcu_nocb_flush_bypass(my_rdp, NULL, jiffies));
raw_spin_lock_rcu_node(my_rnp); /* irqs already disabled. */
/* Leverage recent GPs and set GP for new callbacks. */
needwake = rcu_advance_cbs(my_rnp, rdp) ||
rcu_advance_cbs(my_rnp, my_rdp);
rcu_segcblist_merge(&my_rdp->cblist, &rdp->cblist);
needwake = needwake || rcu_advance_cbs(my_rnp, my_rdp);
rcu_segcblist_disable(&rdp->cblist);
WARN_ON_ONCE(rcu_segcblist_empty(&my_rdp->cblist) !=
!rcu_segcblist_n_cbs(&my_rdp->cblist));
if (rcu_segcblist_is_offloaded(&my_rdp->cblist)) {
raw_spin_unlock_rcu_node(my_rnp); /* irqs remain disabled. */
__call_rcu_nocb_wake(my_rdp, true, flags);
} else {
rcu_nocb_unlock(my_rdp); /* irqs remain disabled. */
raw_spin_unlock_irqrestore_rcu_node(my_rnp, flags);
}
if (needwake)
rcu_gp_kthread_wake();
lockdep_assert_irqs_enabled();
WARN_ONCE(rcu_segcblist_n_cbs(&rdp->cblist) != 0 ||
!rcu_segcblist_empty(&rdp->cblist),
"rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, 1stCB=%p\n",
cpu, rcu_segcblist_n_cbs(&rdp->cblist),
rcu_segcblist_first_cb(&rdp->cblist));
}
#endif
/*
* On non-huge systems, use expedited RCU grace periods to make suspend
* and hibernation run faster.
*/
static int rcu_pm_notify(struct notifier_block *self,
unsigned long action, void *hcpu)
{
switch (action) {
case PM_HIBERNATION_PREPARE:
case PM_SUSPEND_PREPARE:
rcu_expedite_gp();
break;
case PM_POST_HIBERNATION:
case PM_POST_SUSPEND:
rcu_unexpedite_gp();
break;
default:
break;
}
return NOTIFY_OK;
}
/*
* Spawn the kthreads that handle RCU's grace periods.
*/
static int __init rcu_spawn_gp_kthread(void)
{
unsigned long flags;
int kthread_prio_in = kthread_prio;
struct rcu_node *rnp;
struct sched_param sp;
struct task_struct *t;
/* Force priority into range. */
if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 2
&& IS_BUILTIN(CONFIG_RCU_TORTURE_TEST))
kthread_prio = 2;
else if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 1)
kthread_prio = 1;
else if (kthread_prio < 0)
kthread_prio = 0;
else if (kthread_prio > 99)
kthread_prio = 99;
if (kthread_prio != kthread_prio_in)
pr_alert("rcu_spawn_gp_kthread(): Limited prio to %d from %d\n",
kthread_prio, kthread_prio_in);
rcu_scheduler_fully_active = 1;
t = kthread_create(rcu_gp_kthread, NULL, "%s", rcu_state.name);
if (WARN_ONCE(IS_ERR(t), "%s: Could not start grace-period kthread, OOM is now expected behavior\n", __func__))
return 0;
rnp = rcu_get_root();
raw_spin_lock_irqsave_rcu_node(rnp, flags);
rcu_state.gp_kthread = t;
if (kthread_prio) {
sp.sched_priority = kthread_prio;
sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
}
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
wake_up_process(t);
rcu_spawn_nocb_kthreads();
rcu_spawn_boost_kthreads();
return 0;
}
early_initcall(rcu_spawn_gp_kthread);
/*
* This function is invoked towards the end of the scheduler's
* initialization process. Before this is called, the idle task might
* contain synchronous grace-period primitives (during which time, this idle
* task is booting the system, and such primitives are no-ops). After this
* function is called, any synchronous grace-period primitives are run as
* expedited, with the requesting task driving the grace period forward.
* A later core_initcall() rcu_set_runtime_mode() will switch to full
* runtime RCU functionality.
*/
void rcu_scheduler_starting(void)
{
WARN_ON(num_online_cpus() != 1);
WARN_ON(nr_context_switches() > 0);
rcu_test_sync_prims();
rcu_scheduler_active = RCU_SCHEDULER_INIT;
rcu_test_sync_prims();
}
/*
* Helper function for rcu_init() that initializes the rcu_state structure.
*/
static void __init rcu_init_one(void)
{
static const char * const buf[] = RCU_NODE_NAME_INIT;
static const char * const fqs[] = RCU_FQS_NAME_INIT;
static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
int levelspread[RCU_NUM_LVLS]; /* kids/node in each level. */
int cpustride = 1;
int i;
int j;
struct rcu_node *rnp;
BUILD_BUG_ON(RCU_NUM_LVLS > ARRAY_SIZE(buf)); /* Fix buf[] init! */
/* Silence gcc 4.8 false positive about array index out of range. */
if (rcu_num_lvls <= 0 || rcu_num_lvls > RCU_NUM_LVLS)
panic("rcu_init_one: rcu_num_lvls out of range");
/* Initialize the level-tracking arrays. */
for (i = 1; i < rcu_num_lvls; i++)
rcu_state.level[i] =
rcu_state.level[i - 1] + num_rcu_lvl[i - 1];
rcu_init_levelspread(levelspread, num_rcu_lvl);
/* Initialize the elements themselves, starting from the leaves. */
for (i = rcu_num_lvls - 1; i >= 0; i--) {
cpustride *= levelspread[i];
rnp = rcu_state.level[i];
for (j = 0; j < num_rcu_lvl[i]; j++, rnp++) {
raw_spin_lock_init(&ACCESS_PRIVATE(rnp, lock));
lockdep_set_class_and_name(&ACCESS_PRIVATE(rnp, lock),
&rcu_node_class[i], buf[i]);
raw_spin_lock_init(&rnp->fqslock);
lockdep_set_class_and_name(&rnp->fqslock,
&rcu_fqs_class[i], fqs[i]);
rnp->gp_seq = rcu_state.gp_seq;
rnp->gp_seq_needed = rcu_state.gp_seq;
rnp->completedqs = rcu_state.gp_seq;
rnp->qsmask = 0;
rnp->qsmaskinit = 0;
rnp->grplo = j * cpustride;
rnp->grphi = (j + 1) * cpustride - 1;
if (rnp->grphi >= nr_cpu_ids)
rnp->grphi = nr_cpu_ids - 1;
if (i == 0) {
rnp->grpnum = 0;
rnp->grpmask = 0;
rnp->parent = NULL;
} else {
rnp->grpnum = j % levelspread[i - 1];
rnp->grpmask = BIT(rnp->grpnum);
rnp->parent = rcu_state.level[i - 1] +
j / levelspread[i - 1];
}
rnp->level = i;
INIT_LIST_HEAD(&rnp->blkd_tasks);
rcu_init_one_nocb(rnp);
init_waitqueue_head(&rnp->exp_wq[0]);
init_waitqueue_head(&rnp->exp_wq[1]);
init_waitqueue_head(&rnp->exp_wq[2]);
init_waitqueue_head(&rnp->exp_wq[3]);
spin_lock_init(&rnp->exp_lock);
}
}
init_swait_queue_head(&rcu_state.gp_wq);
init_swait_queue_head(&rcu_state.expedited_wq);
rnp = rcu_first_leaf_node();
for_each_possible_cpu(i) {
while (i > rnp->grphi)
rnp++;
per_cpu_ptr(&rcu_data, i)->mynode = rnp;
rcu_boot_init_percpu_data(i);
}
}
/*
* Compute the rcu_node tree geometry from kernel parameters. This cannot
* replace the definitions in tree.h because those are needed to size
* the ->node array in the rcu_state structure.
*/
static void __init rcu_init_geometry(void)
{
ulong d;
int i;
int rcu_capacity[RCU_NUM_LVLS];
/*
* Initialize any unspecified boot parameters.
* The default values of jiffies_till_first_fqs and
* jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS
* value, which is a function of HZ, then adding one for each
* RCU_JIFFIES_FQS_DIV CPUs that might be on the system.
*/
d = RCU_JIFFIES_TILL_FORCE_QS + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
if (jiffies_till_first_fqs == ULONG_MAX)
jiffies_till_first_fqs = d;
if (jiffies_till_next_fqs == ULONG_MAX)
jiffies_till_next_fqs = d;
adjust_jiffies_till_sched_qs();
/* If the compile-time values are accurate, just leave. */
if (rcu_fanout_leaf == RCU_FANOUT_LEAF &&
nr_cpu_ids == NR_CPUS)
return;
pr_info("Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%u\n",
rcu_fanout_leaf, nr_cpu_ids);
/*
* The boot-time rcu_fanout_leaf parameter must be at least two
* and cannot exceed the number of bits in the rcu_node masks.
* Complain and fall back to the compile-time values if this
* limit is exceeded.
*/
if (rcu_fanout_leaf < 2 ||
rcu_fanout_leaf > sizeof(unsigned long) * 8) {
rcu_fanout_leaf = RCU_FANOUT_LEAF;
WARN_ON(1);
return;
}
/*
* Compute number of nodes that can be handled an rcu_node tree
* with the given number of levels.
*/
rcu_capacity[0] = rcu_fanout_leaf;
for (i = 1; i < RCU_NUM_LVLS; i++)
rcu_capacity[i] = rcu_capacity[i - 1] * RCU_FANOUT;
/*
* The tree must be able to accommodate the configured number of CPUs.
* If this limit is exceeded, fall back to the compile-time values.
*/
if (nr_cpu_ids > rcu_capacity[RCU_NUM_LVLS - 1]) {
rcu_fanout_leaf = RCU_FANOUT_LEAF;
WARN_ON(1);
return;
}
/* Calculate the number of levels in the tree. */
for (i = 0; nr_cpu_ids > rcu_capacity[i]; i++) {
}
rcu_num_lvls = i + 1;
/* Calculate the number of rcu_nodes at each level of the tree. */
for (i = 0; i < rcu_num_lvls; i++) {
int cap = rcu_capacity[(rcu_num_lvls - 1) - i];
num_rcu_lvl[i] = DIV_ROUND_UP(nr_cpu_ids, cap);
}
/* Calculate the total number of rcu_node structures. */
rcu_num_nodes = 0;
for (i = 0; i < rcu_num_lvls; i++)
rcu_num_nodes += num_rcu_lvl[i];
}
/*
* Dump out the structure of the rcu_node combining tree associated
* with the rcu_state structure.
*/
static void __init rcu_dump_rcu_node_tree(void)
{
int level = 0;
struct rcu_node *rnp;
pr_info("rcu_node tree layout dump\n");
pr_info(" ");
rcu_for_each_node_breadth_first(rnp) {
if (rnp->level != level) {
pr_cont("\n");
pr_info(" ");
level = rnp->level;
}
pr_cont("%d:%d ^%d ", rnp->grplo, rnp->grphi, rnp->grpnum);
}
pr_cont("\n");
}
struct workqueue_struct *rcu_gp_wq;
struct workqueue_struct *rcu_par_gp_wq;
void __init rcu_init(void)
{
int cpu;
rcu_early_boot_tests();
rcu_bootup_announce();
rcu_init_geometry();
rcu_init_one();
if (dump_tree)
rcu_dump_rcu_node_tree();
if (use_softirq)
open_softirq(RCU_SOFTIRQ, rcu_core_si);
/*
* We don't need protection against CPU-hotplug here because
* this is called early in boot, before either interrupts
* or the scheduler are operational.
*/
pm_notifier(rcu_pm_notify, 0);
for_each_online_cpu(cpu) {
rcutree_prepare_cpu(cpu);
rcu_cpu_starting(cpu);
rcutree_online_cpu(cpu);
}
/* Create workqueue for expedited GPs and for Tree SRCU. */
rcu_gp_wq = alloc_workqueue("rcu_gp", WQ_MEM_RECLAIM, 0);
WARN_ON(!rcu_gp_wq);
rcu_par_gp_wq = alloc_workqueue("rcu_par_gp", WQ_MEM_RECLAIM, 0);
WARN_ON(!rcu_par_gp_wq);
srcu_init();
}
#include "tree_stall.h"
#include "tree_exp.h"
#include "tree_plugin.h"