linux_dsm_epyc7002/kernel/rcu/tree.h

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/*
* Read-Copy Update mechanism for mutual exclusion (tree-based version)
* Internal non-public definitions.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, you can access it online at
* http://www.gnu.org/licenses/gpl-2.0.html.
*
* Copyright IBM Corporation, 2008
*
* Author: Ingo Molnar <mingo@elte.hu>
* Paul E. McKenney <paulmck@linux.vnet.ibm.com>
*/
#include <linux/cache.h>
#include <linux/spinlock.h>
#include <linux/rtmutex.h>
#include <linux/threads.h>
#include <linux/cpumask.h>
#include <linux/seqlock.h>
rcu: Use simple wait queues where possible in rcutree As of commit dae6e64d2bcfd ("rcu: Introduce proper blocking to no-CBs kthreads GP waits") the RCU subsystem started making use of wait queues. Here we convert all additions of RCU wait queues to use simple wait queues, since they don't need the extra overhead of the full wait queue features. Originally this was done for RT kernels[1], since we would get things like... BUG: sleeping function called from invalid context at kernel/rtmutex.c:659 in_atomic(): 1, irqs_disabled(): 1, pid: 8, name: rcu_preempt Pid: 8, comm: rcu_preempt Not tainted Call Trace: [<ffffffff8106c8d0>] __might_sleep+0xd0/0xf0 [<ffffffff817d77b4>] rt_spin_lock+0x24/0x50 [<ffffffff8106fcf6>] __wake_up+0x36/0x70 [<ffffffff810c4542>] rcu_gp_kthread+0x4d2/0x680 [<ffffffff8105f910>] ? __init_waitqueue_head+0x50/0x50 [<ffffffff810c4070>] ? rcu_gp_fqs+0x80/0x80 [<ffffffff8105eabb>] kthread+0xdb/0xe0 [<ffffffff8106b912>] ? finish_task_switch+0x52/0x100 [<ffffffff817e0754>] kernel_thread_helper+0x4/0x10 [<ffffffff8105e9e0>] ? __init_kthread_worker+0x60/0x60 [<ffffffff817e0750>] ? gs_change+0xb/0xb ...and hence simple wait queues were deployed on RT out of necessity (as simple wait uses a raw lock), but mainline might as well take advantage of the more streamline support as well. [1] This is a carry forward of work from v3.10-rt; the original conversion was by Thomas on an earlier -rt version, and Sebastian extended it to additional post-3.10 added RCU waiters; here I've added a commit log and unified the RCU changes into one, and uprev'd it to match mainline RCU. Signed-off-by: Daniel Wagner <daniel.wagner@bmw-carit.de> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: linux-rt-users@vger.kernel.org Cc: Boqun Feng <boqun.feng@gmail.com> Cc: Marcelo Tosatti <mtosatti@redhat.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Link: http://lkml.kernel.org/r/1455871601-27484-6-git-send-email-wagi@monom.org Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2016-02-19 15:46:41 +07:00
#include <linux/swait.h>
#include <linux/stop_machine.h>
#include <linux/rcu_node_tree.h>
#include "rcu_segcblist.h"
/* Communicate arguments to a workqueue handler. */
struct rcu_exp_work {
smp_call_func_t rew_func;
unsigned long rew_s;
struct work_struct rew_work;
};
/* RCU's kthread states for tracing. */
#define RCU_KTHREAD_STOPPED 0
#define RCU_KTHREAD_RUNNING 1
#define RCU_KTHREAD_WAITING 2
#define RCU_KTHREAD_OFFCPU 3
#define RCU_KTHREAD_YIELDING 4
#define RCU_KTHREAD_MAX 4
/*
* Definition for node within the RCU grace-period-detection hierarchy.
*/
struct rcu_node {
raw_spinlock_t __private lock; /* Root rcu_node's lock protects */
/* some rcu_state fields as well as */
/* following. */
unsigned long gp_seq; /* Track rsp->rcu_gp_seq. */
unsigned long gp_seq_needed; /* Track furthest future GP request. */
unsigned long completedqs; /* All QSes done for this node. */
unsigned long qsmask; /* CPUs or groups that need to switch in */
/* order for current grace period to proceed.*/
/* In leaf rcu_node, each bit corresponds to */
/* an rcu_data structure, otherwise, each */
/* bit corresponds to a child rcu_node */
/* structure. */
unsigned long rcu_gp_init_mask; /* Mask of offline CPUs at GP init. */
unsigned long qsmaskinit;
/* Per-GP initial value for qsmask. */
rcu: Process offlining and onlining only at grace-period start Races between CPU hotplug and grace periods can be difficult to resolve, so the ->onoff_mutex is used to exclude the two events. Unfortunately, this means that it is impossible for an outgoing CPU to perform the last bits of its offlining from its last pass through the idle loop, because sleeplocks cannot be acquired in that context. This commit avoids these problems by buffering online and offline events in a new ->qsmaskinitnext field in the leaf rcu_node structures. When a grace period starts, the events accumulated in this mask are applied to the ->qsmaskinit field, and, if needed, up the rcu_node tree. The special case of all CPUs corresponding to a given leaf rcu_node structure being offline while there are still elements in that structure's ->blkd_tasks list is handled using a new ->wait_blkd_tasks field. In this case, propagating the offline bits up the tree is deferred until the beginning of the grace period after all of the tasks have exited their RCU read-side critical sections and removed themselves from the list, at which point the ->wait_blkd_tasks flag is cleared. If one of that leaf rcu_node structure's CPUs comes back online before the list empties, then the ->wait_blkd_tasks flag is simply cleared. This of course means that RCU's notion of which CPUs are offline can be out of date. This is OK because RCU need only wait on CPUs that were online at the time that the grace period started. In addition, RCU's force-quiescent-state actions will handle the case where a CPU goes offline after the grace period starts. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-01-24 12:52:37 +07:00
/* Initialized from ->qsmaskinitnext at the */
/* beginning of each grace period. */
unsigned long qsmaskinitnext;
/* Online CPUs for next grace period. */
unsigned long expmask; /* CPUs or groups that need to check in */
/* to allow the current expedited GP */
/* to complete. */
unsigned long expmaskinit;
/* Per-GP initial values for expmask. */
/* Initialized from ->expmaskinitnext at the */
/* beginning of each expedited GP. */
unsigned long expmaskinitnext;
/* Online CPUs for next expedited GP. */
/* Any CPU that has ever been online will */
/* have its bit set. */
unsigned long ffmask; /* Fully functional CPUs. */
unsigned long grpmask; /* Mask to apply to parent qsmask. */
/* Only one bit will be set in this mask. */
int grplo; /* lowest-numbered CPU or group here. */
int grphi; /* highest-numbered CPU or group here. */
u8 grpnum; /* CPU/group number for next level up. */
u8 level; /* root is at level 0. */
rcu: Process offlining and onlining only at grace-period start Races between CPU hotplug and grace periods can be difficult to resolve, so the ->onoff_mutex is used to exclude the two events. Unfortunately, this means that it is impossible for an outgoing CPU to perform the last bits of its offlining from its last pass through the idle loop, because sleeplocks cannot be acquired in that context. This commit avoids these problems by buffering online and offline events in a new ->qsmaskinitnext field in the leaf rcu_node structures. When a grace period starts, the events accumulated in this mask are applied to the ->qsmaskinit field, and, if needed, up the rcu_node tree. The special case of all CPUs corresponding to a given leaf rcu_node structure being offline while there are still elements in that structure's ->blkd_tasks list is handled using a new ->wait_blkd_tasks field. In this case, propagating the offline bits up the tree is deferred until the beginning of the grace period after all of the tasks have exited their RCU read-side critical sections and removed themselves from the list, at which point the ->wait_blkd_tasks flag is cleared. If one of that leaf rcu_node structure's CPUs comes back online before the list empties, then the ->wait_blkd_tasks flag is simply cleared. This of course means that RCU's notion of which CPUs are offline can be out of date. This is OK because RCU need only wait on CPUs that were online at the time that the grace period started. In addition, RCU's force-quiescent-state actions will handle the case where a CPU goes offline after the grace period starts. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-01-24 12:52:37 +07:00
bool wait_blkd_tasks;/* Necessary to wait for blocked tasks to */
/* exit RCU read-side critical sections */
/* before propagating offline up the */
/* rcu_node tree? */
struct rcu_node *parent;
struct list_head blkd_tasks;
/* Tasks blocked in RCU read-side critical */
/* section. Tasks are placed at the head */
/* of this list and age towards the tail. */
struct list_head *gp_tasks;
/* Pointer to the first task blocking the */
/* current grace period, or NULL if there */
/* is no such task. */
struct list_head *exp_tasks;
/* Pointer to the first task blocking the */
/* current expedited grace period, or NULL */
/* if there is no such task. If there */
/* is no current expedited grace period, */
/* then there can cannot be any such task. */
struct list_head *boost_tasks;
/* Pointer to first task that needs to be */
/* priority boosted, or NULL if no priority */
/* boosting is needed for this rcu_node */
/* structure. If there are no tasks */
/* queued on this rcu_node structure that */
/* are blocking the current grace period, */
/* there can be no such task. */
struct rt_mutex boost_mtx;
/* Used only for the priority-boosting */
/* side effect, not as a lock. */
unsigned long boost_time;
/* When to start boosting (jiffies). */
struct task_struct *boost_kthread_task;
/* kthread that takes care of priority */
/* boosting for this rcu_node structure. */
unsigned int boost_kthread_status;
/* State of boost_kthread_task for tracing. */
#ifdef CONFIG_RCU_NOCB_CPU
rcu: Use simple wait queues where possible in rcutree As of commit dae6e64d2bcfd ("rcu: Introduce proper blocking to no-CBs kthreads GP waits") the RCU subsystem started making use of wait queues. Here we convert all additions of RCU wait queues to use simple wait queues, since they don't need the extra overhead of the full wait queue features. Originally this was done for RT kernels[1], since we would get things like... BUG: sleeping function called from invalid context at kernel/rtmutex.c:659 in_atomic(): 1, irqs_disabled(): 1, pid: 8, name: rcu_preempt Pid: 8, comm: rcu_preempt Not tainted Call Trace: [<ffffffff8106c8d0>] __might_sleep+0xd0/0xf0 [<ffffffff817d77b4>] rt_spin_lock+0x24/0x50 [<ffffffff8106fcf6>] __wake_up+0x36/0x70 [<ffffffff810c4542>] rcu_gp_kthread+0x4d2/0x680 [<ffffffff8105f910>] ? __init_waitqueue_head+0x50/0x50 [<ffffffff810c4070>] ? rcu_gp_fqs+0x80/0x80 [<ffffffff8105eabb>] kthread+0xdb/0xe0 [<ffffffff8106b912>] ? finish_task_switch+0x52/0x100 [<ffffffff817e0754>] kernel_thread_helper+0x4/0x10 [<ffffffff8105e9e0>] ? __init_kthread_worker+0x60/0x60 [<ffffffff817e0750>] ? gs_change+0xb/0xb ...and hence simple wait queues were deployed on RT out of necessity (as simple wait uses a raw lock), but mainline might as well take advantage of the more streamline support as well. [1] This is a carry forward of work from v3.10-rt; the original conversion was by Thomas on an earlier -rt version, and Sebastian extended it to additional post-3.10 added RCU waiters; here I've added a commit log and unified the RCU changes into one, and uprev'd it to match mainline RCU. Signed-off-by: Daniel Wagner <daniel.wagner@bmw-carit.de> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: linux-rt-users@vger.kernel.org Cc: Boqun Feng <boqun.feng@gmail.com> Cc: Marcelo Tosatti <mtosatti@redhat.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Link: http://lkml.kernel.org/r/1455871601-27484-6-git-send-email-wagi@monom.org Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2016-02-19 15:46:41 +07:00
struct swait_queue_head nocb_gp_wq[2];
/* Place for rcu_nocb_kthread() to wait GP. */
#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
raw_spinlock_t fqslock ____cacheline_internodealigned_in_smp;
spinlock_t exp_lock ____cacheline_internodealigned_in_smp;
unsigned long exp_seq_rq;
wait_queue_head_t exp_wq[4];
struct rcu_exp_work rew;
bool exp_need_flush; /* Need to flush workitem? */
} ____cacheline_internodealigned_in_smp;
rcu: Correctly handle sparse possible cpus In many cases in the RCU tree code, we iterate over the set of cpus for a leaf node described by rcu_node::grplo and rcu_node::grphi, checking per-cpu data for each cpu in this range. However, if the set of possible cpus is sparse, some cpus described in this range are not possible, and thus no per-cpu region will have been allocated (or initialised) for them by the generic percpu code. Erroneous accesses to a per-cpu area for these !possible cpus may fault or may hit other data depending on the addressed generated when the erroneous per cpu offset is applied. In practice, both cases have been observed on arm64 hardware (the former being silent, but detectable with additional patches). To avoid issues resulting from this, we must iterate over the set of *possible* cpus for a given leaf node. This patch add a new helper, for_each_leaf_node_possible_cpu, to enable this. As iteration is often intertwined with rcu_node local bitmask manipulation, a new leaf_node_cpu_bit helper is added to make this simpler and more consistent. The RCU tree code is made to use both of these where appropriate. Without this patch, running reboot at a shell can result in an oops like: [ 3369.075979] Unable to handle kernel paging request at virtual address ffffff8008b21b4c [ 3369.083881] pgd = ffffffc3ecdda000 [ 3369.087270] [ffffff8008b21b4c] *pgd=00000083eca48003, *pud=00000083eca48003, *pmd=0000000000000000 [ 3369.096222] Internal error: Oops: 96000007 [#1] PREEMPT SMP [ 3369.101781] Modules linked in: [ 3369.104825] CPU: 2 PID: 1817 Comm: NetworkManager Tainted: G W 4.6.0+ #3 [ 3369.121239] task: ffffffc0fa13e000 ti: ffffffc3eb940000 task.ti: ffffffc3eb940000 [ 3369.128708] PC is at sync_rcu_exp_select_cpus+0x188/0x510 [ 3369.134094] LR is at sync_rcu_exp_select_cpus+0x104/0x510 [ 3369.139479] pc : [<ffffff80081109a8>] lr : [<ffffff8008110924>] pstate: 200001c5 [ 3369.146860] sp : ffffffc3eb9435a0 [ 3369.150162] x29: ffffffc3eb9435a0 x28: ffffff8008be4f88 [ 3369.155465] x27: ffffff8008b66c80 x26: ffffffc3eceb2600 [ 3369.160767] x25: 0000000000000001 x24: ffffff8008be4f88 [ 3369.166070] x23: ffffff8008b51c3c x22: ffffff8008b66c80 [ 3369.171371] x21: 0000000000000001 x20: ffffff8008b21b40 [ 3369.176673] x19: ffffff8008b66c80 x18: 0000000000000000 [ 3369.181975] x17: 0000007fa951a010 x16: ffffff80086a30f0 [ 3369.187278] x15: 0000007fa9505590 x14: 0000000000000000 [ 3369.192580] x13: ffffff8008b51000 x12: ffffffc3eb940000 [ 3369.197882] x11: 0000000000000006 x10: ffffff8008b51b78 [ 3369.203184] x9 : 0000000000000001 x8 : ffffff8008be4000 [ 3369.208486] x7 : ffffff8008b21b40 x6 : 0000000000001003 [ 3369.213788] x5 : 0000000000000000 x4 : ffffff8008b27280 [ 3369.219090] x3 : ffffff8008b21b4c x2 : 0000000000000001 [ 3369.224406] x1 : 0000000000000001 x0 : 0000000000000140 ... [ 3369.972257] [<ffffff80081109a8>] sync_rcu_exp_select_cpus+0x188/0x510 [ 3369.978685] [<ffffff80081128b4>] synchronize_rcu_expedited+0x64/0xa8 [ 3369.985026] [<ffffff80086b987c>] synchronize_net+0x24/0x30 [ 3369.990499] [<ffffff80086ddb54>] dev_deactivate_many+0x28c/0x298 [ 3369.996493] [<ffffff80086b6bb8>] __dev_close_many+0x60/0xd0 [ 3370.002052] [<ffffff80086b6d48>] __dev_close+0x28/0x40 [ 3370.007178] [<ffffff80086bf62c>] __dev_change_flags+0x8c/0x158 [ 3370.012999] [<ffffff80086bf718>] dev_change_flags+0x20/0x60 [ 3370.018558] [<ffffff80086cf7f0>] do_setlink+0x288/0x918 [ 3370.023771] [<ffffff80086d0798>] rtnl_newlink+0x398/0x6a8 [ 3370.029158] [<ffffff80086cee84>] rtnetlink_rcv_msg+0xe4/0x220 [ 3370.034891] [<ffffff80086e274c>] netlink_rcv_skb+0xc4/0xf8 [ 3370.040364] [<ffffff80086ced8c>] rtnetlink_rcv+0x2c/0x40 [ 3370.045663] [<ffffff80086e1fe8>] netlink_unicast+0x160/0x238 [ 3370.051309] [<ffffff80086e24b8>] netlink_sendmsg+0x2f0/0x358 [ 3370.056956] [<ffffff80086a0070>] sock_sendmsg+0x18/0x30 [ 3370.062168] [<ffffff80086a21cc>] ___sys_sendmsg+0x26c/0x280 [ 3370.067728] [<ffffff80086a30ac>] __sys_sendmsg+0x44/0x88 [ 3370.073027] [<ffffff80086a3100>] SyS_sendmsg+0x10/0x20 [ 3370.078153] [<ffffff8008085e70>] el0_svc_naked+0x24/0x28 Signed-off-by: Mark Rutland <mark.rutland@arm.com> Reported-by: Dennis Chen <dennis.chen@arm.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Josh Triplett <josh@joshtriplett.org> Cc: Lai Jiangshan <jiangshanlai@gmail.com> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Steve Capper <steve.capper@arm.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Will Deacon <will.deacon@arm.com> Cc: linux-kernel@vger.kernel.org Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-06-03 21:20:04 +07:00
/*
* Bitmasks in an rcu_node cover the interval [grplo, grphi] of CPU IDs, and
* are indexed relative to this interval rather than the global CPU ID space.
* This generates the bit for a CPU in node-local masks.
*/
#define leaf_node_cpu_bit(rnp, cpu) (BIT((cpu) - (rnp)->grplo))
rcu: Correctly handle sparse possible cpus In many cases in the RCU tree code, we iterate over the set of cpus for a leaf node described by rcu_node::grplo and rcu_node::grphi, checking per-cpu data for each cpu in this range. However, if the set of possible cpus is sparse, some cpus described in this range are not possible, and thus no per-cpu region will have been allocated (or initialised) for them by the generic percpu code. Erroneous accesses to a per-cpu area for these !possible cpus may fault or may hit other data depending on the addressed generated when the erroneous per cpu offset is applied. In practice, both cases have been observed on arm64 hardware (the former being silent, but detectable with additional patches). To avoid issues resulting from this, we must iterate over the set of *possible* cpus for a given leaf node. This patch add a new helper, for_each_leaf_node_possible_cpu, to enable this. As iteration is often intertwined with rcu_node local bitmask manipulation, a new leaf_node_cpu_bit helper is added to make this simpler and more consistent. The RCU tree code is made to use both of these where appropriate. Without this patch, running reboot at a shell can result in an oops like: [ 3369.075979] Unable to handle kernel paging request at virtual address ffffff8008b21b4c [ 3369.083881] pgd = ffffffc3ecdda000 [ 3369.087270] [ffffff8008b21b4c] *pgd=00000083eca48003, *pud=00000083eca48003, *pmd=0000000000000000 [ 3369.096222] Internal error: Oops: 96000007 [#1] PREEMPT SMP [ 3369.101781] Modules linked in: [ 3369.104825] CPU: 2 PID: 1817 Comm: NetworkManager Tainted: G W 4.6.0+ #3 [ 3369.121239] task: ffffffc0fa13e000 ti: ffffffc3eb940000 task.ti: ffffffc3eb940000 [ 3369.128708] PC is at sync_rcu_exp_select_cpus+0x188/0x510 [ 3369.134094] LR is at sync_rcu_exp_select_cpus+0x104/0x510 [ 3369.139479] pc : [<ffffff80081109a8>] lr : [<ffffff8008110924>] pstate: 200001c5 [ 3369.146860] sp : ffffffc3eb9435a0 [ 3369.150162] x29: ffffffc3eb9435a0 x28: ffffff8008be4f88 [ 3369.155465] x27: ffffff8008b66c80 x26: ffffffc3eceb2600 [ 3369.160767] x25: 0000000000000001 x24: ffffff8008be4f88 [ 3369.166070] x23: ffffff8008b51c3c x22: ffffff8008b66c80 [ 3369.171371] x21: 0000000000000001 x20: ffffff8008b21b40 [ 3369.176673] x19: ffffff8008b66c80 x18: 0000000000000000 [ 3369.181975] x17: 0000007fa951a010 x16: ffffff80086a30f0 [ 3369.187278] x15: 0000007fa9505590 x14: 0000000000000000 [ 3369.192580] x13: ffffff8008b51000 x12: ffffffc3eb940000 [ 3369.197882] x11: 0000000000000006 x10: ffffff8008b51b78 [ 3369.203184] x9 : 0000000000000001 x8 : ffffff8008be4000 [ 3369.208486] x7 : ffffff8008b21b40 x6 : 0000000000001003 [ 3369.213788] x5 : 0000000000000000 x4 : ffffff8008b27280 [ 3369.219090] x3 : ffffff8008b21b4c x2 : 0000000000000001 [ 3369.224406] x1 : 0000000000000001 x0 : 0000000000000140 ... [ 3369.972257] [<ffffff80081109a8>] sync_rcu_exp_select_cpus+0x188/0x510 [ 3369.978685] [<ffffff80081128b4>] synchronize_rcu_expedited+0x64/0xa8 [ 3369.985026] [<ffffff80086b987c>] synchronize_net+0x24/0x30 [ 3369.990499] [<ffffff80086ddb54>] dev_deactivate_many+0x28c/0x298 [ 3369.996493] [<ffffff80086b6bb8>] __dev_close_many+0x60/0xd0 [ 3370.002052] [<ffffff80086b6d48>] __dev_close+0x28/0x40 [ 3370.007178] [<ffffff80086bf62c>] __dev_change_flags+0x8c/0x158 [ 3370.012999] [<ffffff80086bf718>] dev_change_flags+0x20/0x60 [ 3370.018558] [<ffffff80086cf7f0>] do_setlink+0x288/0x918 [ 3370.023771] [<ffffff80086d0798>] rtnl_newlink+0x398/0x6a8 [ 3370.029158] [<ffffff80086cee84>] rtnetlink_rcv_msg+0xe4/0x220 [ 3370.034891] [<ffffff80086e274c>] netlink_rcv_skb+0xc4/0xf8 [ 3370.040364] [<ffffff80086ced8c>] rtnetlink_rcv+0x2c/0x40 [ 3370.045663] [<ffffff80086e1fe8>] netlink_unicast+0x160/0x238 [ 3370.051309] [<ffffff80086e24b8>] netlink_sendmsg+0x2f0/0x358 [ 3370.056956] [<ffffff80086a0070>] sock_sendmsg+0x18/0x30 [ 3370.062168] [<ffffff80086a21cc>] ___sys_sendmsg+0x26c/0x280 [ 3370.067728] [<ffffff80086a30ac>] __sys_sendmsg+0x44/0x88 [ 3370.073027] [<ffffff80086a3100>] SyS_sendmsg+0x10/0x20 [ 3370.078153] [<ffffff8008085e70>] el0_svc_naked+0x24/0x28 Signed-off-by: Mark Rutland <mark.rutland@arm.com> Reported-by: Dennis Chen <dennis.chen@arm.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Josh Triplett <josh@joshtriplett.org> Cc: Lai Jiangshan <jiangshanlai@gmail.com> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Steve Capper <steve.capper@arm.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Will Deacon <will.deacon@arm.com> Cc: linux-kernel@vger.kernel.org Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-06-03 21:20:04 +07:00
/*
* Union to allow "aggregate OR" operation on the need for a quiescent
* state by the normal and expedited grace periods.
*/
union rcu_noqs {
struct {
u8 norm;
u8 exp;
} b; /* Bits. */
u16 s; /* Set of bits, aggregate OR here. */
};
/* Per-CPU data for read-copy update. */
struct rcu_data {
/* 1) quiescent-state and grace-period handling : */
unsigned long gp_seq; /* Track rsp->rcu_gp_seq counter. */
unsigned long gp_seq_needed; /* Track furthest future GP request. */
union rcu_noqs cpu_no_qs; /* No QSes yet for this CPU. */
bool core_needs_qs; /* Core waits for quiesc state. */
bool beenonline; /* CPU online at least once. */
bool gpwrap; /* Possible ->gp_seq wrap. */
rcu: Defer reporting RCU-preempt quiescent states when disabled This commit defers reporting of RCU-preempt quiescent states at rcu_read_unlock_special() time when any of interrupts, softirq, or preemption are disabled. These deferred quiescent states are reported at a later RCU_SOFTIRQ, context switch, idle entry, or CPU-hotplug offline operation. Of course, if another RCU read-side critical section has started in the meantime, the reporting of the quiescent state will be further deferred. This also means that disabling preemption, interrupts, and/or softirqs will act as an RCU-preempt read-side critical section. This is enforced by checking preempt_count() as needed. Some special cases must be handled on an ad-hoc basis, for example, context switch is a quiescent state even though both the scheduler and do_exit() disable preemption. In these cases, additional calls to rcu_preempt_deferred_qs() override the preemption disabling. Similar logic overrides disabled interrupts in rcu_preempt_check_callbacks() because in this case the quiescent state happened just before the corresponding scheduling-clock interrupt. In theory, this change lifts a long-standing restriction that required that if interrupts were disabled across a call to rcu_read_unlock() that the matching rcu_read_lock() also be contained within that interrupts-disabled region of code. Because the reporting of the corresponding RCU-preempt quiescent state is now deferred until after interrupts have been enabled, it is no longer possible for this situation to result in deadlocks involving the scheduler's runqueue and priority-inheritance locks. This may allow some code simplification that might reduce interrupt latency a bit. Unfortunately, in practice this would also defer deboosting a low-priority task that had been subjected to RCU priority boosting, so real-time-response considerations might well force this restriction to remain in place. Because RCU-preempt grace periods are now blocked not only by RCU read-side critical sections, but also by disabling of interrupts, preemption, and softirqs, it will be possible to eliminate RCU-bh and RCU-sched in favor of RCU-preempt in CONFIG_PREEMPT=y kernels. This may require some additional plumbing to provide the network denial-of-service guarantees that have been traditionally provided by RCU-bh. Once these are in place, CONFIG_PREEMPT=n kernels will be able to fold RCU-bh into RCU-sched. This would mean that all kernels would have but one flavor of RCU, which would open the door to significant code cleanup. Moving to a single flavor of RCU would also have the beneficial effect of reducing the NOCB kthreads by at least a factor of two. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> [ paulmck: Apply rcu_read_unlock_special() preempt_count() feedback from Joel Fernandes. ] [ paulmck: Adjust rcu_eqs_enter() call to rcu_preempt_deferred_qs() in response to bug reports from kbuild test robot. ] [ paulmck: Fix bug located by kbuild test robot involving recursion via rcu_preempt_deferred_qs(). ]
2018-06-22 02:50:01 +07:00
bool deferred_qs; /* This CPU awaiting a deferred QS? */
struct rcu_node *mynode; /* This CPU's leaf of hierarchy */
unsigned long grpmask; /* Mask to apply to leaf qsmask. */
unsigned long ticks_this_gp; /* The number of scheduling-clock */
/* ticks this CPU has handled */
/* during and after the last grace */
/* period it is aware of. */
/* 2) batch handling */
struct rcu_segcblist cblist; /* Segmented callback list, with */
/* different callbacks waiting for */
/* different grace periods. */
long qlen_last_fqs_check;
/* qlen at last check for QS forcing */
unsigned long n_force_qs_snap;
/* did other CPU force QS recently? */
long blimit; /* Upper limit on a processed batch */
/* 3) dynticks interface. */
int dynticks_snap; /* Per-GP tracking for dynticks. */
long dynticks_nesting; /* Track process nesting level. */
long dynticks_nmi_nesting; /* Track irq/NMI nesting level. */
atomic_t dynticks; /* Even value for idle, else odd. */
bool rcu_need_heavy_qs; /* GP old, so heavy quiescent state! */
bool rcu_urgent_qs; /* GP old need light quiescent state. */
#ifdef CONFIG_RCU_FAST_NO_HZ
bool all_lazy; /* Are all CPU's CBs lazy? */
unsigned long nonlazy_posted; /* # times non-lazy CB posted to CPU. */
unsigned long nonlazy_posted_snap;
/* Nonlazy_posted snapshot. */
unsigned long last_accelerate; /* Last jiffy CBs were accelerated. */
unsigned long last_advance_all; /* Last jiffy CBs were all advanced. */
int tick_nohz_enabled_snap; /* Previously seen value from sysfs. */
#endif /* #ifdef CONFIG_RCU_FAST_NO_HZ */
/* 4) rcu_barrier(), OOM callbacks, and expediting. */
struct rcu_head barrier_head;
int exp_dynticks_snap; /* Double-check need for IPI. */
/* 5) Callback offloading. */
#ifdef CONFIG_RCU_NOCB_CPU
struct rcu_head *nocb_head; /* CBs waiting for kthread. */
struct rcu_head **nocb_tail;
atomic_long_t nocb_q_count; /* # CBs waiting for nocb */
atomic_long_t nocb_q_count_lazy; /* invocation (all stages). */
rcu: Parallelize and economize NOCB kthread wakeups An 80-CPU system with a context-switch-heavy workload can require so many NOCB kthread wakeups that the RCU grace-period kthreads spend several tens of percent of a CPU just awakening things. This clearly will not scale well: If you add enough CPUs, the RCU grace-period kthreads would get behind, increasing grace-period latency. To avoid this problem, this commit divides the NOCB kthreads into leaders and followers, where the grace-period kthreads awaken the leaders each of whom in turn awakens its followers. By default, the number of groups of kthreads is the square root of the number of CPUs, but this default may be overridden using the rcutree.rcu_nocb_leader_stride boot parameter. This reduces the number of wakeups done per grace period by the RCU grace-period kthread by the square root of the number of CPUs, but of course by shifting those wakeups to the leaders. In addition, because the leaders do grace periods on behalf of their respective followers, the number of wakeups of the followers decreases by up to a factor of two. Instead of being awakened once when new callbacks arrive and again at the end of the grace period, the followers are awakened only at the end of the grace period. For a numerical example, in a 4096-CPU system, the grace-period kthread would awaken 64 leaders, each of which would awaken its 63 followers at the end of the grace period. This compares favorably with the 79 wakeups for the grace-period kthread on an 80-CPU system. Reported-by: Rik van Riel <riel@redhat.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2014-06-24 23:26:11 +07:00
struct rcu_head *nocb_follower_head; /* CBs ready to invoke. */
struct rcu_head **nocb_follower_tail;
rcu: Use simple wait queues where possible in rcutree As of commit dae6e64d2bcfd ("rcu: Introduce proper blocking to no-CBs kthreads GP waits") the RCU subsystem started making use of wait queues. Here we convert all additions of RCU wait queues to use simple wait queues, since they don't need the extra overhead of the full wait queue features. Originally this was done for RT kernels[1], since we would get things like... BUG: sleeping function called from invalid context at kernel/rtmutex.c:659 in_atomic(): 1, irqs_disabled(): 1, pid: 8, name: rcu_preempt Pid: 8, comm: rcu_preempt Not tainted Call Trace: [<ffffffff8106c8d0>] __might_sleep+0xd0/0xf0 [<ffffffff817d77b4>] rt_spin_lock+0x24/0x50 [<ffffffff8106fcf6>] __wake_up+0x36/0x70 [<ffffffff810c4542>] rcu_gp_kthread+0x4d2/0x680 [<ffffffff8105f910>] ? __init_waitqueue_head+0x50/0x50 [<ffffffff810c4070>] ? rcu_gp_fqs+0x80/0x80 [<ffffffff8105eabb>] kthread+0xdb/0xe0 [<ffffffff8106b912>] ? finish_task_switch+0x52/0x100 [<ffffffff817e0754>] kernel_thread_helper+0x4/0x10 [<ffffffff8105e9e0>] ? __init_kthread_worker+0x60/0x60 [<ffffffff817e0750>] ? gs_change+0xb/0xb ...and hence simple wait queues were deployed on RT out of necessity (as simple wait uses a raw lock), but mainline might as well take advantage of the more streamline support as well. [1] This is a carry forward of work from v3.10-rt; the original conversion was by Thomas on an earlier -rt version, and Sebastian extended it to additional post-3.10 added RCU waiters; here I've added a commit log and unified the RCU changes into one, and uprev'd it to match mainline RCU. Signed-off-by: Daniel Wagner <daniel.wagner@bmw-carit.de> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: linux-rt-users@vger.kernel.org Cc: Boqun Feng <boqun.feng@gmail.com> Cc: Marcelo Tosatti <mtosatti@redhat.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Link: http://lkml.kernel.org/r/1455871601-27484-6-git-send-email-wagi@monom.org Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2016-02-19 15:46:41 +07:00
struct swait_queue_head nocb_wq; /* For nocb kthreads to sleep on. */
struct task_struct *nocb_kthread;
raw_spinlock_t nocb_lock; /* Guard following pair of fields. */
int nocb_defer_wakeup; /* Defer wakeup of nocb_kthread. */
struct timer_list nocb_timer; /* Enforce finite deferral. */
rcu: Parallelize and economize NOCB kthread wakeups An 80-CPU system with a context-switch-heavy workload can require so many NOCB kthread wakeups that the RCU grace-period kthreads spend several tens of percent of a CPU just awakening things. This clearly will not scale well: If you add enough CPUs, the RCU grace-period kthreads would get behind, increasing grace-period latency. To avoid this problem, this commit divides the NOCB kthreads into leaders and followers, where the grace-period kthreads awaken the leaders each of whom in turn awakens its followers. By default, the number of groups of kthreads is the square root of the number of CPUs, but this default may be overridden using the rcutree.rcu_nocb_leader_stride boot parameter. This reduces the number of wakeups done per grace period by the RCU grace-period kthread by the square root of the number of CPUs, but of course by shifting those wakeups to the leaders. In addition, because the leaders do grace periods on behalf of their respective followers, the number of wakeups of the followers decreases by up to a factor of two. Instead of being awakened once when new callbacks arrive and again at the end of the grace period, the followers are awakened only at the end of the grace period. For a numerical example, in a 4096-CPU system, the grace-period kthread would awaken 64 leaders, each of which would awaken its 63 followers at the end of the grace period. This compares favorably with the 79 wakeups for the grace-period kthread on an 80-CPU system. Reported-by: Rik van Riel <riel@redhat.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2014-06-24 23:26:11 +07:00
/* The following fields are used by the leader, hence own cacheline. */
struct rcu_head *nocb_gp_head ____cacheline_internodealigned_in_smp;
/* CBs waiting for GP. */
struct rcu_head **nocb_gp_tail;
bool nocb_leader_sleep; /* Is the nocb leader thread asleep? */
rcu: Parallelize and economize NOCB kthread wakeups An 80-CPU system with a context-switch-heavy workload can require so many NOCB kthread wakeups that the RCU grace-period kthreads spend several tens of percent of a CPU just awakening things. This clearly will not scale well: If you add enough CPUs, the RCU grace-period kthreads would get behind, increasing grace-period latency. To avoid this problem, this commit divides the NOCB kthreads into leaders and followers, where the grace-period kthreads awaken the leaders each of whom in turn awakens its followers. By default, the number of groups of kthreads is the square root of the number of CPUs, but this default may be overridden using the rcutree.rcu_nocb_leader_stride boot parameter. This reduces the number of wakeups done per grace period by the RCU grace-period kthread by the square root of the number of CPUs, but of course by shifting those wakeups to the leaders. In addition, because the leaders do grace periods on behalf of their respective followers, the number of wakeups of the followers decreases by up to a factor of two. Instead of being awakened once when new callbacks arrive and again at the end of the grace period, the followers are awakened only at the end of the grace period. For a numerical example, in a 4096-CPU system, the grace-period kthread would awaken 64 leaders, each of which would awaken its 63 followers at the end of the grace period. This compares favorably with the 79 wakeups for the grace-period kthread on an 80-CPU system. Reported-by: Rik van Riel <riel@redhat.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2014-06-24 23:26:11 +07:00
struct rcu_data *nocb_next_follower;
/* Next follower in wakeup chain. */
/* The following fields are used by the follower, hence new cachline. */
struct rcu_data *nocb_leader ____cacheline_internodealigned_in_smp;
/* Leader CPU takes GP-end wakeups. */
#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
/* 6) Diagnostic data, including RCU CPU stall warnings. */
unsigned int softirq_snap; /* Snapshot of softirq activity. */
/* ->rcu_iw* fields protected by leaf rcu_node ->lock. */
struct irq_work rcu_iw; /* Check for non-irq activity. */
bool rcu_iw_pending; /* Is ->rcu_iw pending? */
unsigned long rcu_iw_gp_seq; /* ->gp_seq associated with ->rcu_iw. */
unsigned long rcu_ofl_gp_seq; /* ->gp_seq at last offline. */
short rcu_ofl_gp_flags; /* ->gp_flags at last offline. */
unsigned long rcu_onl_gp_seq; /* ->gp_seq at last online. */
short rcu_onl_gp_flags; /* ->gp_flags at last online. */
unsigned long last_fqs_resched; /* Time of last rcu_resched(). */
int cpu;
};
/* Values for nocb_defer_wakeup field in struct rcu_data. */
#define RCU_NOCB_WAKE_NOT 0
#define RCU_NOCB_WAKE 1
#define RCU_NOCB_WAKE_FORCE 2
#define RCU_JIFFIES_TILL_FORCE_QS (1 + (HZ > 250) + (HZ > 500))
/* For jiffies_till_first_fqs and */
/* and jiffies_till_next_fqs. */
#define RCU_JIFFIES_FQS_DIV 256 /* Very large systems need more */
/* delay between bouts of */
/* quiescent-state forcing. */
#define RCU_STALL_RAT_DELAY 2 /* Allow other CPUs time to take */
/* at least one scheduling clock */
/* irq before ratting on them. */
#define rcu_wait(cond) \
do { \
for (;;) { \
set_current_state(TASK_INTERRUPTIBLE); \
if (cond) \
break; \
schedule(); \
} \
__set_current_state(TASK_RUNNING); \
} while (0)
/*
* RCU global state, including node hierarchy. This hierarchy is
* represented in "heap" form in a dense array. The root (first level)
* of the hierarchy is in ->node[0] (referenced by ->level[0]), the second
* level in ->node[1] through ->node[m] (->node[1] referenced by ->level[1]),
* and the third level in ->node[m+1] and following (->node[m+1] referenced
* by ->level[2]). The number of levels is determined by the number of
* CPUs and by CONFIG_RCU_FANOUT. Small systems will have a "hierarchy"
* consisting of a single rcu_node.
*/
struct rcu_state {
struct rcu_node node[NUM_RCU_NODES]; /* Hierarchy. */
struct rcu_node *level[RCU_NUM_LVLS + 1];
/* Hierarchy levels (+1 to */
/* shut bogus gcc warning) */
int ncpus; /* # CPUs seen so far. */
/* The following fields are guarded by the root rcu_node's lock. */
u8 boost ____cacheline_internodealigned_in_smp;
/* Subject to priority boost. */
unsigned long gp_seq; /* Grace-period sequence #. */
struct task_struct *gp_kthread; /* Task for grace periods. */
rcu: Use simple wait queues where possible in rcutree As of commit dae6e64d2bcfd ("rcu: Introduce proper blocking to no-CBs kthreads GP waits") the RCU subsystem started making use of wait queues. Here we convert all additions of RCU wait queues to use simple wait queues, since they don't need the extra overhead of the full wait queue features. Originally this was done for RT kernels[1], since we would get things like... BUG: sleeping function called from invalid context at kernel/rtmutex.c:659 in_atomic(): 1, irqs_disabled(): 1, pid: 8, name: rcu_preempt Pid: 8, comm: rcu_preempt Not tainted Call Trace: [<ffffffff8106c8d0>] __might_sleep+0xd0/0xf0 [<ffffffff817d77b4>] rt_spin_lock+0x24/0x50 [<ffffffff8106fcf6>] __wake_up+0x36/0x70 [<ffffffff810c4542>] rcu_gp_kthread+0x4d2/0x680 [<ffffffff8105f910>] ? __init_waitqueue_head+0x50/0x50 [<ffffffff810c4070>] ? rcu_gp_fqs+0x80/0x80 [<ffffffff8105eabb>] kthread+0xdb/0xe0 [<ffffffff8106b912>] ? finish_task_switch+0x52/0x100 [<ffffffff817e0754>] kernel_thread_helper+0x4/0x10 [<ffffffff8105e9e0>] ? __init_kthread_worker+0x60/0x60 [<ffffffff817e0750>] ? gs_change+0xb/0xb ...and hence simple wait queues were deployed on RT out of necessity (as simple wait uses a raw lock), but mainline might as well take advantage of the more streamline support as well. [1] This is a carry forward of work from v3.10-rt; the original conversion was by Thomas on an earlier -rt version, and Sebastian extended it to additional post-3.10 added RCU waiters; here I've added a commit log and unified the RCU changes into one, and uprev'd it to match mainline RCU. Signed-off-by: Daniel Wagner <daniel.wagner@bmw-carit.de> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: linux-rt-users@vger.kernel.org Cc: Boqun Feng <boqun.feng@gmail.com> Cc: Marcelo Tosatti <mtosatti@redhat.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Link: http://lkml.kernel.org/r/1455871601-27484-6-git-send-email-wagi@monom.org Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2016-02-19 15:46:41 +07:00
struct swait_queue_head gp_wq; /* Where GP task waits. */
short gp_flags; /* Commands for GP task. */
short gp_state; /* GP kthread sleep state. */
/* End of fields guarded by root rcu_node's lock. */
struct mutex barrier_mutex; /* Guards barrier fields. */
atomic_t barrier_cpu_count; /* # CPUs waiting on. */
struct completion barrier_completion; /* Wake at barrier end. */
unsigned long barrier_sequence; /* ++ at start and end of */
/* rcu_barrier(). */
/* End of fields guarded by barrier_mutex. */
struct mutex exp_mutex; /* Serialize expedited GP. */
struct mutex exp_wake_mutex; /* Serialize wakeup. */
unsigned long expedited_sequence; /* Take a ticket. */
atomic_t expedited_need_qs; /* # CPUs left to check in. */
rcu: Use simple wait queues where possible in rcutree As of commit dae6e64d2bcfd ("rcu: Introduce proper blocking to no-CBs kthreads GP waits") the RCU subsystem started making use of wait queues. Here we convert all additions of RCU wait queues to use simple wait queues, since they don't need the extra overhead of the full wait queue features. Originally this was done for RT kernels[1], since we would get things like... BUG: sleeping function called from invalid context at kernel/rtmutex.c:659 in_atomic(): 1, irqs_disabled(): 1, pid: 8, name: rcu_preempt Pid: 8, comm: rcu_preempt Not tainted Call Trace: [<ffffffff8106c8d0>] __might_sleep+0xd0/0xf0 [<ffffffff817d77b4>] rt_spin_lock+0x24/0x50 [<ffffffff8106fcf6>] __wake_up+0x36/0x70 [<ffffffff810c4542>] rcu_gp_kthread+0x4d2/0x680 [<ffffffff8105f910>] ? __init_waitqueue_head+0x50/0x50 [<ffffffff810c4070>] ? rcu_gp_fqs+0x80/0x80 [<ffffffff8105eabb>] kthread+0xdb/0xe0 [<ffffffff8106b912>] ? finish_task_switch+0x52/0x100 [<ffffffff817e0754>] kernel_thread_helper+0x4/0x10 [<ffffffff8105e9e0>] ? __init_kthread_worker+0x60/0x60 [<ffffffff817e0750>] ? gs_change+0xb/0xb ...and hence simple wait queues were deployed on RT out of necessity (as simple wait uses a raw lock), but mainline might as well take advantage of the more streamline support as well. [1] This is a carry forward of work from v3.10-rt; the original conversion was by Thomas on an earlier -rt version, and Sebastian extended it to additional post-3.10 added RCU waiters; here I've added a commit log and unified the RCU changes into one, and uprev'd it to match mainline RCU. Signed-off-by: Daniel Wagner <daniel.wagner@bmw-carit.de> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: linux-rt-users@vger.kernel.org Cc: Boqun Feng <boqun.feng@gmail.com> Cc: Marcelo Tosatti <mtosatti@redhat.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Link: http://lkml.kernel.org/r/1455871601-27484-6-git-send-email-wagi@monom.org Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2016-02-19 15:46:41 +07:00
struct swait_queue_head expedited_wq; /* Wait for check-ins. */
int ncpus_snap; /* # CPUs seen last time. */
unsigned long jiffies_force_qs; /* Time at which to invoke */
/* force_quiescent_state(). */
unsigned long jiffies_kick_kthreads; /* Time at which to kick */
/* kthreads, if configured. */
unsigned long n_force_qs; /* Number of calls to */
/* force_quiescent_state(). */
unsigned long gp_start; /* Time at which GP started, */
/* but in jiffies. */
unsigned long gp_end; /* Time last GP ended, again */
/* in jiffies. */
unsigned long gp_activity; /* Time of last GP kthread */
/* activity in jiffies. */
unsigned long gp_req_activity; /* Time of last GP request */
/* in jiffies. */
unsigned long jiffies_stall; /* Time at which to check */
/* for CPU stalls. */
unsigned long jiffies_resched; /* Time at which to resched */
/* a reluctant CPU. */
unsigned long n_force_qs_gpstart; /* Snapshot of n_force_qs at */
/* GP start. */
unsigned long gp_max; /* Maximum GP duration in */
/* jiffies. */
const char *name; /* Name of structure. */
char abbr; /* Abbreviated name. */
rcu: Fix grace-period hangs due to race with CPU offline Without special fail-safe quiescent-state-propagation checks, grace-period hangs can result from the following scenario: 1. CPU 1 goes offline. 2. Because CPU 1 is the only CPU in the system blocking the current grace period, the grace period ends as soon as rcu_cleanup_dying_idle_cpu()'s call to rcu_report_qs_rnp() returns. 3. At this point, the leaf rcu_node structure's ->lock is no longer held: rcu_report_qs_rnp() has released it, as it must in order to awaken the RCU grace-period kthread. 4. At this point, that same leaf rcu_node structure's ->qsmaskinitnext field still records CPU 1 as being online. This is absolutely necessary because the scheduler uses RCU (in this case on the wake-up path while awakening RCU's grace-period kthread), and ->qsmaskinitnext contains RCU's idea as to which CPUs are online. Therefore, invoking rcu_report_qs_rnp() after clearing CPU 1's bit from ->qsmaskinitnext would result in a lockdep-RCU splat due to RCU being used from an offline CPU. 5. RCU's grace-period kthread awakens, sees that the old grace period has completed and that a new one is needed. It therefore starts a new grace period, but because CPU 1's leaf rcu_node structure's ->qsmaskinitnext field still shows CPU 1 as being online, this new grace period is initialized to wait for a quiescent state from the now-offline CPU 1. 6. Without the fail-safe force-quiescent-state checks, there would be no quiescent state from the now-offline CPU 1, which would eventually result in RCU CPU stall warnings and memory exhaustion. It would be good to get rid of the special fail-safe quiescent-state propagation checks, and thus it would be good to fix things so that the above scenario cannot happen. This commit therefore adds a new ->ofl_lock to the rcu_state structure. This lock is held by rcu_gp_init() across the applying of buffered online and offline operations to the rcu_node tree, and it is also held by rcu_cleanup_dying_idle_cpu() when buffering a new offline operation. This prevents rcu_gp_init() from acquiring the leaf rcu_node structure's lock during the interval between when rcu_cleanup_dying_idle_cpu() invokes rcu_report_qs_rnp(), which releases ->lock and the re-acquisition of that same lock. This in turn prevents the failure scenario outlined above, and will hopefully eventually allow removal of the offline-CPU checks from the force-quiescent-state code path. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-05-26 09:23:09 +07:00
raw_spinlock_t ofl_lock ____cacheline_internodealigned_in_smp;
rcu: Fix grace-period hangs due to race with CPU offline Without special fail-safe quiescent-state-propagation checks, grace-period hangs can result from the following scenario: 1. CPU 1 goes offline. 2. Because CPU 1 is the only CPU in the system blocking the current grace period, the grace period ends as soon as rcu_cleanup_dying_idle_cpu()'s call to rcu_report_qs_rnp() returns. 3. At this point, the leaf rcu_node structure's ->lock is no longer held: rcu_report_qs_rnp() has released it, as it must in order to awaken the RCU grace-period kthread. 4. At this point, that same leaf rcu_node structure's ->qsmaskinitnext field still records CPU 1 as being online. This is absolutely necessary because the scheduler uses RCU (in this case on the wake-up path while awakening RCU's grace-period kthread), and ->qsmaskinitnext contains RCU's idea as to which CPUs are online. Therefore, invoking rcu_report_qs_rnp() after clearing CPU 1's bit from ->qsmaskinitnext would result in a lockdep-RCU splat due to RCU being used from an offline CPU. 5. RCU's grace-period kthread awakens, sees that the old grace period has completed and that a new one is needed. It therefore starts a new grace period, but because CPU 1's leaf rcu_node structure's ->qsmaskinitnext field still shows CPU 1 as being online, this new grace period is initialized to wait for a quiescent state from the now-offline CPU 1. 6. Without the fail-safe force-quiescent-state checks, there would be no quiescent state from the now-offline CPU 1, which would eventually result in RCU CPU stall warnings and memory exhaustion. It would be good to get rid of the special fail-safe quiescent-state propagation checks, and thus it would be good to fix things so that the above scenario cannot happen. This commit therefore adds a new ->ofl_lock to the rcu_state structure. This lock is held by rcu_gp_init() across the applying of buffered online and offline operations to the rcu_node tree, and it is also held by rcu_cleanup_dying_idle_cpu() when buffering a new offline operation. This prevents rcu_gp_init() from acquiring the leaf rcu_node structure's lock during the interval between when rcu_cleanup_dying_idle_cpu() invokes rcu_report_qs_rnp(), which releases ->lock and the re-acquisition of that same lock. This in turn prevents the failure scenario outlined above, and will hopefully eventually allow removal of the offline-CPU checks from the force-quiescent-state code path. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-05-26 09:23:09 +07:00
/* Synchronize offline with */
/* GP pre-initialization. */
};
/* Values for rcu_state structure's gp_flags field. */
#define RCU_GP_FLAG_INIT 0x1 /* Need grace-period initialization. */
#define RCU_GP_FLAG_FQS 0x2 /* Need grace-period quiescent-state forcing. */
/* Values for rcu_state structure's gp_state field. */
#define RCU_GP_IDLE 0 /* Initial state and no GP in progress. */
#define RCU_GP_WAIT_GPS 1 /* Wait for grace-period start. */
#define RCU_GP_DONE_GPS 2 /* Wait done for grace-period start. */
#define RCU_GP_ONOFF 3 /* Grace-period initialization hotplug. */
#define RCU_GP_INIT 4 /* Grace-period initialization. */
#define RCU_GP_WAIT_FQS 5 /* Wait for force-quiescent-state time. */
#define RCU_GP_DOING_FQS 6 /* Wait done for force-quiescent-state time. */
#define RCU_GP_CLEANUP 7 /* Grace-period cleanup started. */
#define RCU_GP_CLEANED 8 /* Grace-period cleanup complete. */
static const char * const gp_state_names[] = {
"RCU_GP_IDLE",
"RCU_GP_WAIT_GPS",
"RCU_GP_DONE_GPS",
"RCU_GP_ONOFF",
"RCU_GP_INIT",
"RCU_GP_WAIT_FQS",
"RCU_GP_DOING_FQS",
"RCU_GP_CLEANUP",
"RCU_GP_CLEANED",
};
/*
* In order to export the rcu_state name to the tracing tools, it
* needs to be added in the __tracepoint_string section.
* This requires defining a separate variable tp_<sname>_varname
* that points to the string being used, and this will allow
* the tracing userspace tools to be able to decipher the string
* address to the matching string.
*/
#ifdef CONFIG_PREEMPT_RCU
#define RCU_ABBR 'p'
#define RCU_NAME_RAW "rcu_preempt"
#else /* #ifdef CONFIG_PREEMPT_RCU */
#define RCU_ABBR 's'
#define RCU_NAME_RAW "rcu_sched"
#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
#ifndef CONFIG_TRACING
#define RCU_NAME RCU_NAME_RAW
#else /* #ifdef CONFIG_TRACING */
static char rcu_name[] = RCU_NAME_RAW;
static const char *tp_rcu_varname __used __tracepoint_string = rcu_name;
#define RCU_NAME rcu_name
#endif /* #else #ifdef CONFIG_TRACING */
int rcu_dynticks_snap(struct rcu_data *rdp);
#ifdef CONFIG_RCU_BOOST
DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
DECLARE_PER_CPU(int, rcu_cpu_kthread_cpu);
DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
DECLARE_PER_CPU(char, rcu_cpu_has_work);
#endif /* #ifdef CONFIG_RCU_BOOST */
/* Forward declarations for rcutree_plugin.h */
static void rcu_bootup_announce(void);
static void rcu_qs(void);
static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp);
rcu: Fix grace-period-stall bug on large systems with CPU hotplug When the last CPU of a given leaf rcu_node structure goes offline, all of the tasks queued on that leaf rcu_node structure (due to having blocked in their current RCU read-side critical sections) are requeued onto the root rcu_node structure. This requeuing is carried out by rcu_preempt_offline_tasks(). However, it is possible that these queued tasks are the only thing preventing the leaf rcu_node structure from reporting a quiescent state up the rcu_node hierarchy. Unfortunately, the old code would fail to do this reporting, resulting in a grace-period stall given the following sequence of events: 1. Kernel built for more than 32 CPUs on 32-bit systems or for more than 64 CPUs on 64-bit systems, so that there is more than one rcu_node structure. (Or CONFIG_RCU_FANOUT is artificially set to a number smaller than CONFIG_NR_CPUS.) 2. The kernel is built with CONFIG_TREE_PREEMPT_RCU. 3. A task running on a CPU associated with a given leaf rcu_node structure blocks while in an RCU read-side critical section -and- that CPU has not yet passed through a quiescent state for the current RCU grace period. This will cause the task to be queued on the leaf rcu_node's blocked_tasks[] array, in particular, on the element of this array corresponding to the current grace period. 4. Each of the remaining CPUs corresponding to this same leaf rcu_node structure pass through a quiescent state. However, the task is still in its RCU read-side critical section, so these quiescent states cannot be reported further up the rcu_node hierarchy. Nevertheless, all bits in the leaf rcu_node structure's ->qsmask field are now zero. 5. Each of the remaining CPUs go offline. (The events in step #4 and #5 can happen in any order as long as each CPU passes through a quiescent state before going offline.) 6. When the last CPU goes offline, __rcu_offline_cpu() will invoke rcu_preempt_offline_tasks(), which will move the task to the root rcu_node structure, but without reporting a quiescent state up the rcu_node hierarchy (and this failure to report a quiescent state is the bug). But because this leaf rcu_node structure's ->qsmask field is already zero and its ->block_tasks[] entries are all empty, force_quiescent_state() will skip this rcu_node structure. Therefore, grace periods are now hung. This patch abstracts some code out of rcu_read_unlock_special(), calling the result task_quiet() by analogy with cpu_quiet(), and invokes task_quiet() from both rcu_read_lock_special() and __rcu_offline_cpu(). Invoking task_quiet() from __rcu_offline_cpu() reports the quiescent state up the rcu_node hierarchy, fixing the bug. This ends up requiring a separate lock_class_key per level of the rcu_node hierarchy, which this patch also provides. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12589088301770-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-11-22 23:53:48 +07:00
#ifdef CONFIG_HOTPLUG_CPU
static bool rcu_preempt_has_tasks(struct rcu_node *rnp);
rcu: Fix grace-period-stall bug on large systems with CPU hotplug When the last CPU of a given leaf rcu_node structure goes offline, all of the tasks queued on that leaf rcu_node structure (due to having blocked in their current RCU read-side critical sections) are requeued onto the root rcu_node structure. This requeuing is carried out by rcu_preempt_offline_tasks(). However, it is possible that these queued tasks are the only thing preventing the leaf rcu_node structure from reporting a quiescent state up the rcu_node hierarchy. Unfortunately, the old code would fail to do this reporting, resulting in a grace-period stall given the following sequence of events: 1. Kernel built for more than 32 CPUs on 32-bit systems or for more than 64 CPUs on 64-bit systems, so that there is more than one rcu_node structure. (Or CONFIG_RCU_FANOUT is artificially set to a number smaller than CONFIG_NR_CPUS.) 2. The kernel is built with CONFIG_TREE_PREEMPT_RCU. 3. A task running on a CPU associated with a given leaf rcu_node structure blocks while in an RCU read-side critical section -and- that CPU has not yet passed through a quiescent state for the current RCU grace period. This will cause the task to be queued on the leaf rcu_node's blocked_tasks[] array, in particular, on the element of this array corresponding to the current grace period. 4. Each of the remaining CPUs corresponding to this same leaf rcu_node structure pass through a quiescent state. However, the task is still in its RCU read-side critical section, so these quiescent states cannot be reported further up the rcu_node hierarchy. Nevertheless, all bits in the leaf rcu_node structure's ->qsmask field are now zero. 5. Each of the remaining CPUs go offline. (The events in step #4 and #5 can happen in any order as long as each CPU passes through a quiescent state before going offline.) 6. When the last CPU goes offline, __rcu_offline_cpu() will invoke rcu_preempt_offline_tasks(), which will move the task to the root rcu_node structure, but without reporting a quiescent state up the rcu_node hierarchy (and this failure to report a quiescent state is the bug). But because this leaf rcu_node structure's ->qsmask field is already zero and its ->block_tasks[] entries are all empty, force_quiescent_state() will skip this rcu_node structure. Therefore, grace periods are now hung. This patch abstracts some code out of rcu_read_unlock_special(), calling the result task_quiet() by analogy with cpu_quiet(), and invokes task_quiet() from both rcu_read_lock_special() and __rcu_offline_cpu(). Invoking task_quiet() from __rcu_offline_cpu() reports the quiescent state up the rcu_node hierarchy, fixing the bug. This ends up requiring a separate lock_class_key per level of the rcu_node hierarchy, which this patch also provides. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12589088301770-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-11-22 23:53:48 +07:00
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
static void rcu_print_detail_task_stall(void);
static int rcu_print_task_stall(struct rcu_node *rnp);
static int rcu_print_task_exp_stall(struct rcu_node *rnp);
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp);
static void rcu_flavor_check_callbacks(int user);
void call_rcu(struct rcu_head *head, rcu_callback_t func);
static void dump_blkd_tasks(struct rcu_node *rnp, int ncheck);
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags);
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp);
static void invoke_rcu_callbacks_kthread(void);
static bool rcu_is_callbacks_kthread(void);
static void __init rcu_spawn_boost_kthreads(void);
static void rcu_prepare_kthreads(int cpu);
static void rcu_cleanup_after_idle(void);
static void rcu_prepare_for_idle(void);
static void rcu_idle_count_callbacks_posted(void);
rcu: Process offlining and onlining only at grace-period start Races between CPU hotplug and grace periods can be difficult to resolve, so the ->onoff_mutex is used to exclude the two events. Unfortunately, this means that it is impossible for an outgoing CPU to perform the last bits of its offlining from its last pass through the idle loop, because sleeplocks cannot be acquired in that context. This commit avoids these problems by buffering online and offline events in a new ->qsmaskinitnext field in the leaf rcu_node structures. When a grace period starts, the events accumulated in this mask are applied to the ->qsmaskinit field, and, if needed, up the rcu_node tree. The special case of all CPUs corresponding to a given leaf rcu_node structure being offline while there are still elements in that structure's ->blkd_tasks list is handled using a new ->wait_blkd_tasks field. In this case, propagating the offline bits up the tree is deferred until the beginning of the grace period after all of the tasks have exited their RCU read-side critical sections and removed themselves from the list, at which point the ->wait_blkd_tasks flag is cleared. If one of that leaf rcu_node structure's CPUs comes back online before the list empties, then the ->wait_blkd_tasks flag is simply cleared. This of course means that RCU's notion of which CPUs are offline can be out of date. This is OK because RCU need only wait on CPUs that were online at the time that the grace period started. In addition, RCU's force-quiescent-state actions will handle the case where a CPU goes offline after the grace period starts. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-01-24 12:52:37 +07:00
static bool rcu_preempt_has_tasks(struct rcu_node *rnp);
rcu: Defer reporting RCU-preempt quiescent states when disabled This commit defers reporting of RCU-preempt quiescent states at rcu_read_unlock_special() time when any of interrupts, softirq, or preemption are disabled. These deferred quiescent states are reported at a later RCU_SOFTIRQ, context switch, idle entry, or CPU-hotplug offline operation. Of course, if another RCU read-side critical section has started in the meantime, the reporting of the quiescent state will be further deferred. This also means that disabling preemption, interrupts, and/or softirqs will act as an RCU-preempt read-side critical section. This is enforced by checking preempt_count() as needed. Some special cases must be handled on an ad-hoc basis, for example, context switch is a quiescent state even though both the scheduler and do_exit() disable preemption. In these cases, additional calls to rcu_preempt_deferred_qs() override the preemption disabling. Similar logic overrides disabled interrupts in rcu_preempt_check_callbacks() because in this case the quiescent state happened just before the corresponding scheduling-clock interrupt. In theory, this change lifts a long-standing restriction that required that if interrupts were disabled across a call to rcu_read_unlock() that the matching rcu_read_lock() also be contained within that interrupts-disabled region of code. Because the reporting of the corresponding RCU-preempt quiescent state is now deferred until after interrupts have been enabled, it is no longer possible for this situation to result in deadlocks involving the scheduler's runqueue and priority-inheritance locks. This may allow some code simplification that might reduce interrupt latency a bit. Unfortunately, in practice this would also defer deboosting a low-priority task that had been subjected to RCU priority boosting, so real-time-response considerations might well force this restriction to remain in place. Because RCU-preempt grace periods are now blocked not only by RCU read-side critical sections, but also by disabling of interrupts, preemption, and softirqs, it will be possible to eliminate RCU-bh and RCU-sched in favor of RCU-preempt in CONFIG_PREEMPT=y kernels. This may require some additional plumbing to provide the network denial-of-service guarantees that have been traditionally provided by RCU-bh. Once these are in place, CONFIG_PREEMPT=n kernels will be able to fold RCU-bh into RCU-sched. This would mean that all kernels would have but one flavor of RCU, which would open the door to significant code cleanup. Moving to a single flavor of RCU would also have the beneficial effect of reducing the NOCB kthreads by at least a factor of two. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> [ paulmck: Apply rcu_read_unlock_special() preempt_count() feedback from Joel Fernandes. ] [ paulmck: Adjust rcu_eqs_enter() call to rcu_preempt_deferred_qs() in response to bug reports from kbuild test robot. ] [ paulmck: Fix bug located by kbuild test robot involving recursion via rcu_preempt_deferred_qs(). ]
2018-06-22 02:50:01 +07:00
static bool rcu_preempt_need_deferred_qs(struct task_struct *t);
static void rcu_preempt_deferred_qs(struct task_struct *t);
static void print_cpu_stall_info_begin(void);
static void print_cpu_stall_info(int cpu);
static void print_cpu_stall_info_end(void);
static void zero_cpu_stall_ticks(struct rcu_data *rdp);
static bool rcu_nocb_cpu_needs_barrier(int cpu);
rcu: Use simple wait queues where possible in rcutree As of commit dae6e64d2bcfd ("rcu: Introduce proper blocking to no-CBs kthreads GP waits") the RCU subsystem started making use of wait queues. Here we convert all additions of RCU wait queues to use simple wait queues, since they don't need the extra overhead of the full wait queue features. Originally this was done for RT kernels[1], since we would get things like... BUG: sleeping function called from invalid context at kernel/rtmutex.c:659 in_atomic(): 1, irqs_disabled(): 1, pid: 8, name: rcu_preempt Pid: 8, comm: rcu_preempt Not tainted Call Trace: [<ffffffff8106c8d0>] __might_sleep+0xd0/0xf0 [<ffffffff817d77b4>] rt_spin_lock+0x24/0x50 [<ffffffff8106fcf6>] __wake_up+0x36/0x70 [<ffffffff810c4542>] rcu_gp_kthread+0x4d2/0x680 [<ffffffff8105f910>] ? __init_waitqueue_head+0x50/0x50 [<ffffffff810c4070>] ? rcu_gp_fqs+0x80/0x80 [<ffffffff8105eabb>] kthread+0xdb/0xe0 [<ffffffff8106b912>] ? finish_task_switch+0x52/0x100 [<ffffffff817e0754>] kernel_thread_helper+0x4/0x10 [<ffffffff8105e9e0>] ? __init_kthread_worker+0x60/0x60 [<ffffffff817e0750>] ? gs_change+0xb/0xb ...and hence simple wait queues were deployed on RT out of necessity (as simple wait uses a raw lock), but mainline might as well take advantage of the more streamline support as well. [1] This is a carry forward of work from v3.10-rt; the original conversion was by Thomas on an earlier -rt version, and Sebastian extended it to additional post-3.10 added RCU waiters; here I've added a commit log and unified the RCU changes into one, and uprev'd it to match mainline RCU. Signed-off-by: Daniel Wagner <daniel.wagner@bmw-carit.de> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: linux-rt-users@vger.kernel.org Cc: Boqun Feng <boqun.feng@gmail.com> Cc: Marcelo Tosatti <mtosatti@redhat.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Link: http://lkml.kernel.org/r/1455871601-27484-6-git-send-email-wagi@monom.org Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2016-02-19 15:46:41 +07:00
static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp);
static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq);
static void rcu_init_one_nocb(struct rcu_node *rnp);
static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
rcu: Break call_rcu() deadlock involving scheduler and perf Dave Jones got the following lockdep splat: > ====================================================== > [ INFO: possible circular locking dependency detected ] > 3.12.0-rc3+ #92 Not tainted > ------------------------------------------------------- > trinity-child2/15191 is trying to acquire lock: > (&rdp->nocb_wq){......}, at: [<ffffffff8108ff43>] __wake_up+0x23/0x50 > > but task is already holding lock: > (&ctx->lock){-.-...}, at: [<ffffffff81154c19>] perf_event_exit_task+0x109/0x230 > > which lock already depends on the new lock. > > > the existing dependency chain (in reverse order) is: > > -> #3 (&ctx->lock){-.-...}: > [<ffffffff810cc243>] lock_acquire+0x93/0x200 > [<ffffffff81733f90>] _raw_spin_lock+0x40/0x80 > [<ffffffff811500ff>] __perf_event_task_sched_out+0x2df/0x5e0 > [<ffffffff81091b83>] perf_event_task_sched_out+0x93/0xa0 > [<ffffffff81732052>] __schedule+0x1d2/0xa20 > [<ffffffff81732f30>] preempt_schedule_irq+0x50/0xb0 > [<ffffffff817352b6>] retint_kernel+0x26/0x30 > [<ffffffff813eed04>] tty_flip_buffer_push+0x34/0x50 > [<ffffffff813f0504>] pty_write+0x54/0x60 > [<ffffffff813e900d>] n_tty_write+0x32d/0x4e0 > [<ffffffff813e5838>] tty_write+0x158/0x2d0 > [<ffffffff811c4850>] vfs_write+0xc0/0x1f0 > [<ffffffff811c52cc>] SyS_write+0x4c/0xa0 > [<ffffffff8173d4e4>] tracesys+0xdd/0xe2 > > -> #2 (&rq->lock){-.-.-.}: > [<ffffffff810cc243>] lock_acquire+0x93/0x200 > [<ffffffff81733f90>] _raw_spin_lock+0x40/0x80 > [<ffffffff810980b2>] wake_up_new_task+0xc2/0x2e0 > [<ffffffff81054336>] do_fork+0x126/0x460 > [<ffffffff81054696>] kernel_thread+0x26/0x30 > [<ffffffff8171ff93>] rest_init+0x23/0x140 > [<ffffffff81ee1e4b>] start_kernel+0x3f6/0x403 > [<ffffffff81ee1571>] x86_64_start_reservations+0x2a/0x2c > [<ffffffff81ee1664>] x86_64_start_kernel+0xf1/0xf4 > > -> #1 (&p->pi_lock){-.-.-.}: > [<ffffffff810cc243>] lock_acquire+0x93/0x200 > [<ffffffff8173419b>] _raw_spin_lock_irqsave+0x4b/0x90 > [<ffffffff810979d1>] try_to_wake_up+0x31/0x350 > [<ffffffff81097d62>] default_wake_function+0x12/0x20 > [<ffffffff81084af8>] autoremove_wake_function+0x18/0x40 > [<ffffffff8108ea38>] __wake_up_common+0x58/0x90 > [<ffffffff8108ff59>] __wake_up+0x39/0x50 > [<ffffffff8110d4f8>] __call_rcu_nocb_enqueue+0xa8/0xc0 > [<ffffffff81111450>] __call_rcu+0x140/0x820 > [<ffffffff81111b8d>] call_rcu+0x1d/0x20 > [<ffffffff81093697>] cpu_attach_domain+0x287/0x360 > [<ffffffff81099d7e>] build_sched_domains+0xe5e/0x10a0 > [<ffffffff81efa7fc>] sched_init_smp+0x3b7/0x47a > [<ffffffff81ee1f4e>] kernel_init_freeable+0xf6/0x202 > [<ffffffff817200be>] kernel_init+0xe/0x190 > [<ffffffff8173d22c>] ret_from_fork+0x7c/0xb0 > > -> #0 (&rdp->nocb_wq){......}: > [<ffffffff810cb7ca>] __lock_acquire+0x191a/0x1be0 > [<ffffffff810cc243>] lock_acquire+0x93/0x200 > [<ffffffff8173419b>] _raw_spin_lock_irqsave+0x4b/0x90 > [<ffffffff8108ff43>] __wake_up+0x23/0x50 > [<ffffffff8110d4f8>] __call_rcu_nocb_enqueue+0xa8/0xc0 > [<ffffffff81111450>] __call_rcu+0x140/0x820 > [<ffffffff81111bb0>] kfree_call_rcu+0x20/0x30 > [<ffffffff81149abf>] put_ctx+0x4f/0x70 > [<ffffffff81154c3e>] perf_event_exit_task+0x12e/0x230 > [<ffffffff81056b8d>] do_exit+0x30d/0xcc0 > [<ffffffff8105893c>] do_group_exit+0x4c/0xc0 > [<ffffffff810589c4>] SyS_exit_group+0x14/0x20 > [<ffffffff8173d4e4>] tracesys+0xdd/0xe2 > > other info that might help us debug this: > > Chain exists of: > &rdp->nocb_wq --> &rq->lock --> &ctx->lock > > Possible unsafe locking scenario: > > CPU0 CPU1 > ---- ---- > lock(&ctx->lock); > lock(&rq->lock); > lock(&ctx->lock); > lock(&rdp->nocb_wq); > > *** DEADLOCK *** > > 1 lock held by trinity-child2/15191: > #0: (&ctx->lock){-.-...}, at: [<ffffffff81154c19>] perf_event_exit_task+0x109/0x230 > > stack backtrace: > CPU: 2 PID: 15191 Comm: trinity-child2 Not tainted 3.12.0-rc3+ #92 > ffffffff82565b70 ffff880070c2dbf8 ffffffff8172a363 ffffffff824edf40 > ffff880070c2dc38 ffffffff81726741 ffff880070c2dc90 ffff88022383b1c0 > ffff88022383aac0 0000000000000000 ffff88022383b188 ffff88022383b1c0 > Call Trace: > [<ffffffff8172a363>] dump_stack+0x4e/0x82 > [<ffffffff81726741>] print_circular_bug+0x200/0x20f > [<ffffffff810cb7ca>] __lock_acquire+0x191a/0x1be0 > [<ffffffff810c6439>] ? get_lock_stats+0x19/0x60 > [<ffffffff8100b2f4>] ? native_sched_clock+0x24/0x80 > [<ffffffff810cc243>] lock_acquire+0x93/0x200 > [<ffffffff8108ff43>] ? __wake_up+0x23/0x50 > [<ffffffff8173419b>] _raw_spin_lock_irqsave+0x4b/0x90 > [<ffffffff8108ff43>] ? __wake_up+0x23/0x50 > [<ffffffff8108ff43>] __wake_up+0x23/0x50 > [<ffffffff8110d4f8>] __call_rcu_nocb_enqueue+0xa8/0xc0 > [<ffffffff81111450>] __call_rcu+0x140/0x820 > [<ffffffff8109bc8f>] ? local_clock+0x3f/0x50 > [<ffffffff81111bb0>] kfree_call_rcu+0x20/0x30 > [<ffffffff81149abf>] put_ctx+0x4f/0x70 > [<ffffffff81154c3e>] perf_event_exit_task+0x12e/0x230 > [<ffffffff81056b8d>] do_exit+0x30d/0xcc0 > [<ffffffff810c9af5>] ? trace_hardirqs_on_caller+0x115/0x1e0 > [<ffffffff810c9bcd>] ? trace_hardirqs_on+0xd/0x10 > [<ffffffff8105893c>] do_group_exit+0x4c/0xc0 > [<ffffffff810589c4>] SyS_exit_group+0x14/0x20 > [<ffffffff8173d4e4>] tracesys+0xdd/0xe2 The underlying problem is that perf is invoking call_rcu() with the scheduler locks held, but in NOCB mode, call_rcu() will with high probability invoke the scheduler -- which just might want to use its locks. The reason that call_rcu() needs to invoke the scheduler is to wake up the corresponding rcuo callback-offload kthread, which does the job of starting up a grace period and invoking the callbacks afterwards. One solution (championed on a related problem by Lai Jiangshan) is to simply defer the wakeup to some point where scheduler locks are no longer held. Since we don't want to unnecessarily incur the cost of such deferral, the task before us is threefold: 1. Determine when it is likely that a relevant scheduler lock is held. 2. Defer the wakeup in such cases. 3. Ensure that all deferred wakeups eventually happen, preferably sooner rather than later. We use irqs_disabled_flags() as a proxy for relevant scheduler locks being held. This works because the relevant locks are always acquired with interrupts disabled. We may defer more often than needed, but that is at least safe. The wakeup deferral is tracked via a new field in the per-CPU and per-RCU-flavor rcu_data structure, namely ->nocb_defer_wakeup. This flag is checked by the RCU core processing. The __rcu_pending() function now checks this flag, which causes rcu_check_callbacks() to initiate RCU core processing at each scheduling-clock interrupt where this flag is set. Of course this is not sufficient because scheduling-clock interrupts are often turned off (the things we used to be able to count on!). So the flags are also checked on entry to any state that RCU considers to be idle, which includes both NO_HZ_IDLE idle state and NO_HZ_FULL user-mode-execution state. This approach should allow call_rcu() to be invoked regardless of what locks you might be holding, the key word being "should". Reported-by: Dave Jones <davej@redhat.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org>
2013-10-05 04:33:34 +07:00
bool lazy, unsigned long flags);
static bool rcu_nocb_adopt_orphan_cbs(struct rcu_data *my_rdp,
rcu: Break call_rcu() deadlock involving scheduler and perf Dave Jones got the following lockdep splat: > ====================================================== > [ INFO: possible circular locking dependency detected ] > 3.12.0-rc3+ #92 Not tainted > ------------------------------------------------------- > trinity-child2/15191 is trying to acquire lock: > (&rdp->nocb_wq){......}, at: [<ffffffff8108ff43>] __wake_up+0x23/0x50 > > but task is already holding lock: > (&ctx->lock){-.-...}, at: [<ffffffff81154c19>] perf_event_exit_task+0x109/0x230 > > which lock already depends on the new lock. > > > the existing dependency chain (in reverse order) is: > > -> #3 (&ctx->lock){-.-...}: > [<ffffffff810cc243>] lock_acquire+0x93/0x200 > [<ffffffff81733f90>] _raw_spin_lock+0x40/0x80 > [<ffffffff811500ff>] __perf_event_task_sched_out+0x2df/0x5e0 > [<ffffffff81091b83>] perf_event_task_sched_out+0x93/0xa0 > [<ffffffff81732052>] __schedule+0x1d2/0xa20 > [<ffffffff81732f30>] preempt_schedule_irq+0x50/0xb0 > [<ffffffff817352b6>] retint_kernel+0x26/0x30 > [<ffffffff813eed04>] tty_flip_buffer_push+0x34/0x50 > [<ffffffff813f0504>] pty_write+0x54/0x60 > [<ffffffff813e900d>] n_tty_write+0x32d/0x4e0 > [<ffffffff813e5838>] tty_write+0x158/0x2d0 > [<ffffffff811c4850>] vfs_write+0xc0/0x1f0 > [<ffffffff811c52cc>] SyS_write+0x4c/0xa0 > [<ffffffff8173d4e4>] tracesys+0xdd/0xe2 > > -> #2 (&rq->lock){-.-.-.}: > [<ffffffff810cc243>] lock_acquire+0x93/0x200 > [<ffffffff81733f90>] _raw_spin_lock+0x40/0x80 > [<ffffffff810980b2>] wake_up_new_task+0xc2/0x2e0 > [<ffffffff81054336>] do_fork+0x126/0x460 > [<ffffffff81054696>] kernel_thread+0x26/0x30 > [<ffffffff8171ff93>] rest_init+0x23/0x140 > [<ffffffff81ee1e4b>] start_kernel+0x3f6/0x403 > [<ffffffff81ee1571>] x86_64_start_reservations+0x2a/0x2c > [<ffffffff81ee1664>] x86_64_start_kernel+0xf1/0xf4 > > -> #1 (&p->pi_lock){-.-.-.}: > [<ffffffff810cc243>] lock_acquire+0x93/0x200 > [<ffffffff8173419b>] _raw_spin_lock_irqsave+0x4b/0x90 > [<ffffffff810979d1>] try_to_wake_up+0x31/0x350 > [<ffffffff81097d62>] default_wake_function+0x12/0x20 > [<ffffffff81084af8>] autoremove_wake_function+0x18/0x40 > [<ffffffff8108ea38>] __wake_up_common+0x58/0x90 > [<ffffffff8108ff59>] __wake_up+0x39/0x50 > [<ffffffff8110d4f8>] __call_rcu_nocb_enqueue+0xa8/0xc0 > [<ffffffff81111450>] __call_rcu+0x140/0x820 > [<ffffffff81111b8d>] call_rcu+0x1d/0x20 > [<ffffffff81093697>] cpu_attach_domain+0x287/0x360 > [<ffffffff81099d7e>] build_sched_domains+0xe5e/0x10a0 > [<ffffffff81efa7fc>] sched_init_smp+0x3b7/0x47a > [<ffffffff81ee1f4e>] kernel_init_freeable+0xf6/0x202 > [<ffffffff817200be>] kernel_init+0xe/0x190 > [<ffffffff8173d22c>] ret_from_fork+0x7c/0xb0 > > -> #0 (&rdp->nocb_wq){......}: > [<ffffffff810cb7ca>] __lock_acquire+0x191a/0x1be0 > [<ffffffff810cc243>] lock_acquire+0x93/0x200 > [<ffffffff8173419b>] _raw_spin_lock_irqsave+0x4b/0x90 > [<ffffffff8108ff43>] __wake_up+0x23/0x50 > [<ffffffff8110d4f8>] __call_rcu_nocb_enqueue+0xa8/0xc0 > [<ffffffff81111450>] __call_rcu+0x140/0x820 > [<ffffffff81111bb0>] kfree_call_rcu+0x20/0x30 > [<ffffffff81149abf>] put_ctx+0x4f/0x70 > [<ffffffff81154c3e>] perf_event_exit_task+0x12e/0x230 > [<ffffffff81056b8d>] do_exit+0x30d/0xcc0 > [<ffffffff8105893c>] do_group_exit+0x4c/0xc0 > [<ffffffff810589c4>] SyS_exit_group+0x14/0x20 > [<ffffffff8173d4e4>] tracesys+0xdd/0xe2 > > other info that might help us debug this: > > Chain exists of: > &rdp->nocb_wq --> &rq->lock --> &ctx->lock > > Possible unsafe locking scenario: > > CPU0 CPU1 > ---- ---- > lock(&ctx->lock); > lock(&rq->lock); > lock(&ctx->lock); > lock(&rdp->nocb_wq); > > *** DEADLOCK *** > > 1 lock held by trinity-child2/15191: > #0: (&ctx->lock){-.-...}, at: [<ffffffff81154c19>] perf_event_exit_task+0x109/0x230 > > stack backtrace: > CPU: 2 PID: 15191 Comm: trinity-child2 Not tainted 3.12.0-rc3+ #92 > ffffffff82565b70 ffff880070c2dbf8 ffffffff8172a363 ffffffff824edf40 > ffff880070c2dc38 ffffffff81726741 ffff880070c2dc90 ffff88022383b1c0 > ffff88022383aac0 0000000000000000 ffff88022383b188 ffff88022383b1c0 > Call Trace: > [<ffffffff8172a363>] dump_stack+0x4e/0x82 > [<ffffffff81726741>] print_circular_bug+0x200/0x20f > [<ffffffff810cb7ca>] __lock_acquire+0x191a/0x1be0 > [<ffffffff810c6439>] ? get_lock_stats+0x19/0x60 > [<ffffffff8100b2f4>] ? native_sched_clock+0x24/0x80 > [<ffffffff810cc243>] lock_acquire+0x93/0x200 > [<ffffffff8108ff43>] ? __wake_up+0x23/0x50 > [<ffffffff8173419b>] _raw_spin_lock_irqsave+0x4b/0x90 > [<ffffffff8108ff43>] ? __wake_up+0x23/0x50 > [<ffffffff8108ff43>] __wake_up+0x23/0x50 > [<ffffffff8110d4f8>] __call_rcu_nocb_enqueue+0xa8/0xc0 > [<ffffffff81111450>] __call_rcu+0x140/0x820 > [<ffffffff8109bc8f>] ? local_clock+0x3f/0x50 > [<ffffffff81111bb0>] kfree_call_rcu+0x20/0x30 > [<ffffffff81149abf>] put_ctx+0x4f/0x70 > [<ffffffff81154c3e>] perf_event_exit_task+0x12e/0x230 > [<ffffffff81056b8d>] do_exit+0x30d/0xcc0 > [<ffffffff810c9af5>] ? trace_hardirqs_on_caller+0x115/0x1e0 > [<ffffffff810c9bcd>] ? trace_hardirqs_on+0xd/0x10 > [<ffffffff8105893c>] do_group_exit+0x4c/0xc0 > [<ffffffff810589c4>] SyS_exit_group+0x14/0x20 > [<ffffffff8173d4e4>] tracesys+0xdd/0xe2 The underlying problem is that perf is invoking call_rcu() with the scheduler locks held, but in NOCB mode, call_rcu() will with high probability invoke the scheduler -- which just might want to use its locks. The reason that call_rcu() needs to invoke the scheduler is to wake up the corresponding rcuo callback-offload kthread, which does the job of starting up a grace period and invoking the callbacks afterwards. One solution (championed on a related problem by Lai Jiangshan) is to simply defer the wakeup to some point where scheduler locks are no longer held. Since we don't want to unnecessarily incur the cost of such deferral, the task before us is threefold: 1. Determine when it is likely that a relevant scheduler lock is held. 2. Defer the wakeup in such cases. 3. Ensure that all deferred wakeups eventually happen, preferably sooner rather than later. We use irqs_disabled_flags() as a proxy for relevant scheduler locks being held. This works because the relevant locks are always acquired with interrupts disabled. We may defer more often than needed, but that is at least safe. The wakeup deferral is tracked via a new field in the per-CPU and per-RCU-flavor rcu_data structure, namely ->nocb_defer_wakeup. This flag is checked by the RCU core processing. The __rcu_pending() function now checks this flag, which causes rcu_check_callbacks() to initiate RCU core processing at each scheduling-clock interrupt where this flag is set. Of course this is not sufficient because scheduling-clock interrupts are often turned off (the things we used to be able to count on!). So the flags are also checked on entry to any state that RCU considers to be idle, which includes both NO_HZ_IDLE idle state and NO_HZ_FULL user-mode-execution state. This approach should allow call_rcu() to be invoked regardless of what locks you might be holding, the key word being "should". Reported-by: Dave Jones <davej@redhat.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org>
2013-10-05 04:33:34 +07:00
struct rcu_data *rdp,
unsigned long flags);
static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp);
rcu: Break call_rcu() deadlock involving scheduler and perf Dave Jones got the following lockdep splat: > ====================================================== > [ INFO: possible circular locking dependency detected ] > 3.12.0-rc3+ #92 Not tainted > ------------------------------------------------------- > trinity-child2/15191 is trying to acquire lock: > (&rdp->nocb_wq){......}, at: [<ffffffff8108ff43>] __wake_up+0x23/0x50 > > but task is already holding lock: > (&ctx->lock){-.-...}, at: [<ffffffff81154c19>] perf_event_exit_task+0x109/0x230 > > which lock already depends on the new lock. > > > the existing dependency chain (in reverse order) is: > > -> #3 (&ctx->lock){-.-...}: > [<ffffffff810cc243>] lock_acquire+0x93/0x200 > [<ffffffff81733f90>] _raw_spin_lock+0x40/0x80 > [<ffffffff811500ff>] __perf_event_task_sched_out+0x2df/0x5e0 > [<ffffffff81091b83>] perf_event_task_sched_out+0x93/0xa0 > [<ffffffff81732052>] __schedule+0x1d2/0xa20 > [<ffffffff81732f30>] preempt_schedule_irq+0x50/0xb0 > [<ffffffff817352b6>] retint_kernel+0x26/0x30 > [<ffffffff813eed04>] tty_flip_buffer_push+0x34/0x50 > [<ffffffff813f0504>] pty_write+0x54/0x60 > [<ffffffff813e900d>] n_tty_write+0x32d/0x4e0 > [<ffffffff813e5838>] tty_write+0x158/0x2d0 > [<ffffffff811c4850>] vfs_write+0xc0/0x1f0 > [<ffffffff811c52cc>] SyS_write+0x4c/0xa0 > [<ffffffff8173d4e4>] tracesys+0xdd/0xe2 > > -> #2 (&rq->lock){-.-.-.}: > [<ffffffff810cc243>] lock_acquire+0x93/0x200 > [<ffffffff81733f90>] _raw_spin_lock+0x40/0x80 > [<ffffffff810980b2>] wake_up_new_task+0xc2/0x2e0 > [<ffffffff81054336>] do_fork+0x126/0x460 > [<ffffffff81054696>] kernel_thread+0x26/0x30 > [<ffffffff8171ff93>] rest_init+0x23/0x140 > [<ffffffff81ee1e4b>] start_kernel+0x3f6/0x403 > [<ffffffff81ee1571>] x86_64_start_reservations+0x2a/0x2c > [<ffffffff81ee1664>] x86_64_start_kernel+0xf1/0xf4 > > -> #1 (&p->pi_lock){-.-.-.}: > [<ffffffff810cc243>] lock_acquire+0x93/0x200 > [<ffffffff8173419b>] _raw_spin_lock_irqsave+0x4b/0x90 > [<ffffffff810979d1>] try_to_wake_up+0x31/0x350 > [<ffffffff81097d62>] default_wake_function+0x12/0x20 > [<ffffffff81084af8>] autoremove_wake_function+0x18/0x40 > [<ffffffff8108ea38>] __wake_up_common+0x58/0x90 > [<ffffffff8108ff59>] __wake_up+0x39/0x50 > [<ffffffff8110d4f8>] __call_rcu_nocb_enqueue+0xa8/0xc0 > [<ffffffff81111450>] __call_rcu+0x140/0x820 > [<ffffffff81111b8d>] call_rcu+0x1d/0x20 > [<ffffffff81093697>] cpu_attach_domain+0x287/0x360 > [<ffffffff81099d7e>] build_sched_domains+0xe5e/0x10a0 > [<ffffffff81efa7fc>] sched_init_smp+0x3b7/0x47a > [<ffffffff81ee1f4e>] kernel_init_freeable+0xf6/0x202 > [<ffffffff817200be>] kernel_init+0xe/0x190 > [<ffffffff8173d22c>] ret_from_fork+0x7c/0xb0 > > -> #0 (&rdp->nocb_wq){......}: > [<ffffffff810cb7ca>] __lock_acquire+0x191a/0x1be0 > [<ffffffff810cc243>] lock_acquire+0x93/0x200 > [<ffffffff8173419b>] _raw_spin_lock_irqsave+0x4b/0x90 > [<ffffffff8108ff43>] __wake_up+0x23/0x50 > [<ffffffff8110d4f8>] __call_rcu_nocb_enqueue+0xa8/0xc0 > [<ffffffff81111450>] __call_rcu+0x140/0x820 > [<ffffffff81111bb0>] kfree_call_rcu+0x20/0x30 > [<ffffffff81149abf>] put_ctx+0x4f/0x70 > [<ffffffff81154c3e>] perf_event_exit_task+0x12e/0x230 > [<ffffffff81056b8d>] do_exit+0x30d/0xcc0 > [<ffffffff8105893c>] do_group_exit+0x4c/0xc0 > [<ffffffff810589c4>] SyS_exit_group+0x14/0x20 > [<ffffffff8173d4e4>] tracesys+0xdd/0xe2 > > other info that might help us debug this: > > Chain exists of: > &rdp->nocb_wq --> &rq->lock --> &ctx->lock > > Possible unsafe locking scenario: > > CPU0 CPU1 > ---- ---- > lock(&ctx->lock); > lock(&rq->lock); > lock(&ctx->lock); > lock(&rdp->nocb_wq); > > *** DEADLOCK *** > > 1 lock held by trinity-child2/15191: > #0: (&ctx->lock){-.-...}, at: [<ffffffff81154c19>] perf_event_exit_task+0x109/0x230 > > stack backtrace: > CPU: 2 PID: 15191 Comm: trinity-child2 Not tainted 3.12.0-rc3+ #92 > ffffffff82565b70 ffff880070c2dbf8 ffffffff8172a363 ffffffff824edf40 > ffff880070c2dc38 ffffffff81726741 ffff880070c2dc90 ffff88022383b1c0 > ffff88022383aac0 0000000000000000 ffff88022383b188 ffff88022383b1c0 > Call Trace: > [<ffffffff8172a363>] dump_stack+0x4e/0x82 > [<ffffffff81726741>] print_circular_bug+0x200/0x20f > [<ffffffff810cb7ca>] __lock_acquire+0x191a/0x1be0 > [<ffffffff810c6439>] ? get_lock_stats+0x19/0x60 > [<ffffffff8100b2f4>] ? native_sched_clock+0x24/0x80 > [<ffffffff810cc243>] lock_acquire+0x93/0x200 > [<ffffffff8108ff43>] ? __wake_up+0x23/0x50 > [<ffffffff8173419b>] _raw_spin_lock_irqsave+0x4b/0x90 > [<ffffffff8108ff43>] ? __wake_up+0x23/0x50 > [<ffffffff8108ff43>] __wake_up+0x23/0x50 > [<ffffffff8110d4f8>] __call_rcu_nocb_enqueue+0xa8/0xc0 > [<ffffffff81111450>] __call_rcu+0x140/0x820 > [<ffffffff8109bc8f>] ? local_clock+0x3f/0x50 > [<ffffffff81111bb0>] kfree_call_rcu+0x20/0x30 > [<ffffffff81149abf>] put_ctx+0x4f/0x70 > [<ffffffff81154c3e>] perf_event_exit_task+0x12e/0x230 > [<ffffffff81056b8d>] do_exit+0x30d/0xcc0 > [<ffffffff810c9af5>] ? trace_hardirqs_on_caller+0x115/0x1e0 > [<ffffffff810c9bcd>] ? trace_hardirqs_on+0xd/0x10 > [<ffffffff8105893c>] do_group_exit+0x4c/0xc0 > [<ffffffff810589c4>] SyS_exit_group+0x14/0x20 > [<ffffffff8173d4e4>] tracesys+0xdd/0xe2 The underlying problem is that perf is invoking call_rcu() with the scheduler locks held, but in NOCB mode, call_rcu() will with high probability invoke the scheduler -- which just might want to use its locks. The reason that call_rcu() needs to invoke the scheduler is to wake up the corresponding rcuo callback-offload kthread, which does the job of starting up a grace period and invoking the callbacks afterwards. One solution (championed on a related problem by Lai Jiangshan) is to simply defer the wakeup to some point where scheduler locks are no longer held. Since we don't want to unnecessarily incur the cost of such deferral, the task before us is threefold: 1. Determine when it is likely that a relevant scheduler lock is held. 2. Defer the wakeup in such cases. 3. Ensure that all deferred wakeups eventually happen, preferably sooner rather than later. We use irqs_disabled_flags() as a proxy for relevant scheduler locks being held. This works because the relevant locks are always acquired with interrupts disabled. We may defer more often than needed, but that is at least safe. The wakeup deferral is tracked via a new field in the per-CPU and per-RCU-flavor rcu_data structure, namely ->nocb_defer_wakeup. This flag is checked by the RCU core processing. The __rcu_pending() function now checks this flag, which causes rcu_check_callbacks() to initiate RCU core processing at each scheduling-clock interrupt where this flag is set. Of course this is not sufficient because scheduling-clock interrupts are often turned off (the things we used to be able to count on!). So the flags are also checked on entry to any state that RCU considers to be idle, which includes both NO_HZ_IDLE idle state and NO_HZ_FULL user-mode-execution state. This approach should allow call_rcu() to be invoked regardless of what locks you might be holding, the key word being "should". Reported-by: Dave Jones <davej@redhat.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org>
2013-10-05 04:33:34 +07:00
static void do_nocb_deferred_wakeup(struct rcu_data *rdp);
static void rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp);
static void rcu_spawn_all_nocb_kthreads(int cpu);
static void __init rcu_spawn_nocb_kthreads(void);
#ifdef CONFIG_RCU_NOCB_CPU
static void __init rcu_organize_nocb_kthreads(void);
#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
static bool init_nocb_callback_list(struct rcu_data *rdp);
static unsigned long rcu_get_n_cbs_nocb_cpu(struct rcu_data *rdp);
static void rcu_bind_gp_kthread(void);
static bool rcu_nohz_full_cpu(void);
static void rcu_dynticks_task_enter(void);
static void rcu_dynticks_task_exit(void);
srcu: Parallelize callback handling Peter Zijlstra proposed using SRCU to reduce mmap_sem contention [1,2], however, there are workloads that could result in a high volume of concurrent invocations of call_srcu(), which with current SRCU would result in excessive lock contention on the srcu_struct structure's ->queue_lock, which protects SRCU's callback lists. This commit therefore moves SRCU to per-CPU callback lists, thus greatly reducing contention. Because a given SRCU instance no longer has a single centralized callback list, starting grace periods and invoking callbacks are both more complex than in the single-list Classic SRCU implementation. Starting grace periods and handling callbacks are now handled using an srcu_node tree that is in some ways similar to the rcu_node trees used by RCU-bh, RCU-preempt, and RCU-sched (for example, the srcu_node tree shape is controlled by exactly the same Kconfig options and boot parameters that control the shape of the rcu_node tree). In addition, the old per-CPU srcu_array structure is now named srcu_data and contains an rcu_segcblist structure named ->srcu_cblist for its callbacks (and a spinlock to protect this). The srcu_struct gets an srcu_gp_seq that is used to associate callback segments with the corresponding completion-time grace-period number. These completion-time grace-period numbers are propagated up the srcu_node tree so that the grace-period workqueue handler can determine whether additional grace periods are needed on the one hand and where to look for callbacks that are ready to be invoked. The srcu_barrier() function must now wait on all instances of the per-CPU ->srcu_cblist. Because each ->srcu_cblist is protected by ->lock, srcu_barrier() can remotely add the needed callbacks. In theory, it could also remotely start grace periods, but in practice doing so is complex and racy. And interestingly enough, it is never necessary for srcu_barrier() to start a grace period because srcu_barrier() only enqueues a callback when a callback is already present--and it turns out that a grace period has to have already been started for this pre-existing callback. Furthermore, it is only the callback that srcu_barrier() needs to wait on, not any particular grace period. Therefore, a new rcu_segcblist_entrain() function enqueues the srcu_barrier() function's callback into the same segment occupied by the last pre-existing callback in the list. The special case where all the pre-existing callbacks are on a different list (because they are in the process of being invoked) is handled by enqueuing srcu_barrier()'s callback into the RCU_DONE_TAIL segment, relying on the done-callbacks check that takes place after all callbacks are inovked. Note that the readers use the same algorithm as before. Note that there is a separate srcu_idx that tells the readers what counter to increment. This unfortunately cannot be combined with srcu_gp_seq because they need to be incremented at different times. This commit introduces some ugly #ifdefs in rcutorture. These will go away when I feel good enough about Tree SRCU to ditch Classic SRCU. Some crude performance comparisons, courtesy of a quickly hacked rcuperf asynchronous-grace-period capability: Callback Queuing Overhead ------------------------- # CPUS Classic SRCU Tree SRCU ------ ------------ --------- 2 0.349 us 0.342 us 16 31.66 us 0.4 us 41 --------- 0.417 us The times are the 90th percentiles, a statistic that was chosen to reject the overheads of the occasional srcu_barrier() call needed to avoid OOMing the test machine. The rcuperf test hangs when running Classic SRCU at 41 CPUs, hence the line of dashes. Despite the hacks to both the rcuperf code and that statistics, this is a convincing demonstration of Tree SRCU's performance and scalability advantages. [1] https://lwn.net/Articles/309030/ [2] https://patchwork.kernel.org/patch/5108281/ Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> [ paulmck: Fix initialization if synchronize_srcu_expedited() called first. ]
2017-04-05 23:01:53 +07:00
#ifdef CONFIG_SRCU
void srcu_online_cpu(unsigned int cpu);
void srcu_offline_cpu(unsigned int cpu);
#else /* #ifdef CONFIG_SRCU */
void srcu_online_cpu(unsigned int cpu) { }
void srcu_offline_cpu(unsigned int cpu) { }
#endif /* #else #ifdef CONFIG_SRCU */