kfree_rcu()'s debug_objects logic uses the address of the object's
embedded rcu_head to queue/unqueue. Instead of this, make use of the
object's address itself as preparation for future headless kfree_rcu()
support.
Reviewed-by: Uladzislau Rezki <urezki@gmail.com>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
It is possible that one of the channels cannot be detached
because its free channel is busy and previously queued data
has not been processed yet. On the other hand, another
channel can be successfully detached causing the monitor
work to stop.
Prevent that by rescheduling the monitor work if there are
any channels in the pending state after a detach attempt.
Fixes: 34c8817455 ("rcu: Support kfree_bulk() interface in kfree_rcu()")
Acked-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
To keep the kfree_rcu() code working in purely atomic sections on RT,
such as non-threaded IRQ handlers and raw spinlock sections, avoid
calling into the page allocator which uses sleeping locks on RT.
In fact, even if the caller is preemptible, the kfree_rcu() code is
not, as the krcp->lock is a raw spinlock.
Calling into the page allocator is optional and avoiding it should be
Ok, especially with the page pre-allocation support in future patches.
Such pre-allocation would further avoid the a need for a dynamically
allocated page in the first place.
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Uladzislau Rezki <urezki@gmail.com>
Co-developed-by: Uladzislau Rezki <urezki@gmail.com>
Signed-off-by: Uladzislau Rezki <urezki@gmail.com>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
On PREEMPT_RT kernels, the krcp spinlock gets converted to an rt-mutex
and causes kfree_rcu() callers to sleep. This makes it unusable for
callers in purely atomic sections such as non-threaded IRQ handlers and
raw spinlock sections. Fix it by converting the spinlock to a raw
spinlock.
Vetting all code paths, there is no reason to believe that the raw
spinlock will hurt RT latencies as it is not held for a long time.
Cc: bigeasy@linutronix.de
Cc: Uladzislau Rezki <urezki@gmail.com>
Reviewed-by: Uladzislau Rezki <urezki@gmail.com>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
There are some kernel-doc warnings:
./kernel/rcu/tree.c:2915: warning: Function parameter or member 'count' not described in 'kfree_rcu_cpu'
This commit therefore moves the comment for "count" to the kernel-doc
markup.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Fix kernel-doc warning:
../kernel/rcu/tree.c:959: warning: Excess function parameter 'irq' description in 'rcu_nmi_enter'
Fixes: cf7614e13c ("rcu: Refactor rcu_{nmi,irq}_{enter,exit}()")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Byungchul Park <byungchul.park@lge.com>
Cc: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The ->grpnum field in the rcu_node structure contains the bit position
in this structure's parent's bitmasks, which is not the CPU number.
This commit therefore adjusts this field's comment accordingly.
Signed-off-by: Wei Yang <richard.weiyang@linux.alibaba.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The ->grplo and ->grphi fields store the lowest and highest CPU number
covered by to a rcu_node structure, which is not the group number.
This commit therefore adjusts these fields' comments to match reality.
Signed-off-by: Wei Yang <richard.weiyang@linux.alibaba.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Because gp_max is protected by root rcu_node's lock, this commit moves
the gp_max definition to the region of the rcu_node structure containing
fields protected by this lock.
Signed-off-by: Wei Yang <richard.weiyang@linux.alibaba.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The count and scan can be separated in time, and there is a fair chance
that all work is already done when the scan starts, which might in turn
result in a needless retry. This commit therefore avoids this retry by
returning SHRINK_STOP.
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Peter Enderborg <peter.enderborg@sony.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Coccinelle reports a warning
WARNING: Assignment of 0/1 to bool variable
The root cause is that the variable lastphase is a bool, but is
initialised with integer 1. This commit therefore replaces the 1 with
a true.
Signed-off-by: Jules Irenge <jbi.octave@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The objtool complains about the call to rcu_cleanup_after_idle() from
rcu_nmi_enter(), so this commit adds instrumentation_begin() before that
call and instrumentation_end() after it.
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit removes the variable rnp from check_slow_task(), which
is defined, assigned to, but not otherwise used.
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit converts the schedule_timeout_uninterruptible() call used
by RCU's expedited grace-period processing to schedule_timeout_idle().
This conversion avoids polluting the load-average with RCU-related
sleeping.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit converts the schedule_timeout_interruptible() call used by
RCU's no-CBs grace-period kthreads to schedule_timeout_idle(). This
conversion avoids polluting the load-average with RCU-related sleeping.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit converts the long-standing schedule_timeout_interruptible()
call used by RCU's priority-boosting kthreads to schedule_timeout_idle().
This conversion avoids polluting the load-average with RCU-related
sleeping.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit converts the long-standing schedule_timeout_interruptible()
and schedule_timeout_uninterruptible() calls used by RCU's grace-period
kthread to schedule_timeout_idle(). This conversion avoids polluting
the load-average with RCU-related sleeping.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The rcu_callback_map lockdep_map structure was added back in 2013, but
its purpose has become obscure. This commit therefore documments that the
purpose of rcu_callback map is, in the words of commit 24ef659a85 ("rcu:
Provide better diagnostics for blocking in RCU callback functions"),
to help lockdep to tie an "inappropriate voluntary context switch back
to the fact that the function is being invoked from within a callback."
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit adds a count of the callbacks invoked to the per-CPU rcu_data
structure. This count is printed by the show_rcu_gp_kthreads() that
is invoked by rcutorture and the RCU CPU stall-warning code. It is also
intended for use by drgn.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
There is only 1 bit set in mask, which means that the only difference
between oldmask and the new one will be at the position where the bit is
set in mask. This commit therefore updates rcu_state.ncpus by checking
whether the bit in mask is already set in rnp->expmaskinitnext.
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The __wait_rcu_gp() function unconditionally initializes and cleans up
each element of rs_array[], whether used or not. This is slightly
wasteful and rather confusing, so this commit skips both initialization
and cleanup for duplicate callback functions.
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
- Add a SPDX header;
- Adjust document and section titles;
- Fix list markups;
- Some whitespace fixes and new line breaks;
- Mark literal blocks as such;
- Add it to RCU/index.rst.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
- Add a SPDX header;
- Adjust document and section titles;
- Some whitespace fixes and new line breaks;
- Mark literal blocks as such;
- Add it to RCU/index.rst.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
A KCSAN build revealed we have explicit annoations through atomic_*()
usage, switch to arch_atomic_*() for the respective functions.
vmlinux.o: warning: objtool: rcu_nmi_exit()+0x4d: call to __kcsan_check_access() leaves .noinstr.text section
vmlinux.o: warning: objtool: rcu_dynticks_eqs_enter()+0x25: call to __kcsan_check_access() leaves .noinstr.text section
vmlinux.o: warning: objtool: rcu_nmi_enter()+0x4f: call to __kcsan_check_access() leaves .noinstr.text section
vmlinux.o: warning: objtool: rcu_dynticks_eqs_exit()+0x2a: call to __kcsan_check_access() leaves .noinstr.text section
vmlinux.o: warning: objtool: __rcu_is_watching()+0x25: call to __kcsan_check_access() leaves .noinstr.text section
Additionally, without the NOP in instrumentation_begin(), objtool would
not detect the lack of the 'else instrumentation_begin();' branch in
rcu_nmi_enter().
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Ingo suggested that since the new sched_set_*() functions are
implemented using the 'nocheck' variants, they really shouldn't ever
fail, so remove the return value.
Cc: axboe@kernel.dk
Cc: daniel.lezcano@linaro.org
Cc: sudeep.holla@arm.com
Cc: airlied@redhat.com
Cc: broonie@kernel.org
Cc: paulmck@kernel.org
Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Because SCHED_FIFO is a broken scheduler model (see previous patches)
take away the priority field, the kernel can't possibly make an
informed decision.
Effectively no change.
Cc: paulmck@kernel.org
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Because SCHED_FIFO is a broken scheduler model (see previous patches)
take away the priority field, the kernel can't possibly make an
informed decision.
Effectively no change.
Cc: paulmck@kernel.org
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Here is the tty and serial driver updates for 5.8-rc1
Nothing huge at all, just a lot of little serial driver fixes, updates
for new devices and features, and other small things. Full details are
in the shortlog.
Note, you will get a conflict merging with your tree in the
Documentation/devicetree/bindings/serial/rs485.yaml file, but it should
be pretty obvious what to do. If not, I'm sure Rob will clean it all up
afterwards :)
All of these have been in linux-next with no issues for a while.
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-----BEGIN PGP SIGNATURE-----
iG0EABECAC0WIQT0tgzFv3jCIUoxPcsxR9QN2y37KQUCXtzpCg8cZ3JlZ0Brcm9h
aC5jb20ACgkQMUfUDdst+ylRxACgjGtOKPjahONL4lWd0F8ZYEcyw7sAn34woBCO
BDUV3kolrRQ4OYNJWsHP
=TvqG
-----END PGP SIGNATURE-----
Merge tag 'tty-5.8-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty
Pull tty/serial driver updates from Greg KH:
"Here is the tty and serial driver updates for 5.8-rc1
Nothing huge at all, just a lot of little serial driver fixes, updates
for new devices and features, and other small things. Full details are
in the shortlog.
All of these have been in linux-next with no issues for a while"
* tag 'tty-5.8-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty: (67 commits)
tty: serial: qcom_geni_serial: Add 51.2MHz frequency support
tty: serial: imx: clear Ageing Timer Interrupt in handler
serial: 8250_fintek: Add F81966 Support
sc16is7xx: Add flag to activate IrDA mode
dt-bindings: sc16is7xx: Add flag to activate IrDA mode
serial: 8250: Support rs485 bus termination GPIO
serial: 8520_port: Fix function param documentation
dt-bindings: serial: Add binding for rs485 bus termination GPIO
vt: keyboard: avoid signed integer overflow in k_ascii
serial: 8250: Enable 16550A variants by default on non-x86
tty: hvc_console, fix crashes on parallel open/close
serial: imx: Initialize lock for non-registered console
sc16is7xx: Read the LSR register for basic device presence check
sc16is7xx: Allow sharing the IRQ line
sc16is7xx: Use threaded IRQ
sc16is7xx: Always use falling edge IRQ
tty: n_gsm: Fix bogus i++ in gsm_data_kick
tty: n_gsm: Remove unnecessary test in gsm_print_packet()
serial: stm32: add no_console_suspend support
tty: serial: fsl_lpuart: Use __maybe_unused instead of #if CONFIG_PM_SLEEP
...
Using "%zu" to fix following warning,
kernel/rcu/rcuperf.c: In function ‘kfree_perf_init’:
include/linux/kern_levels.h:5:18: warning: format ‘%lu’ expects argument of type ‘long unsigned int’, but argument 2 has type ‘unsigned int’ [-Wformat=]
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Current RCU hard relies on smp_call_function() callbacks running from
interrupt context. A pending optimization is going to break that, it
will allow idle CPUs to run the callbacks from the idle loop. This
avoids raising the IPI on the requesting CPU and avoids handling an
exception on the receiving CPU.
Change rcu_is_cpu_rrupt_from_idle() to also accept task context,
provided it is the idle task.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Link: https://lore.kernel.org/r/20200527171236.GC706495@hirez.programming.kicks-ass.net
Provide a debug check which can be invoked from exception return to kernel
mode before an attempt is made to schedule. Warn if RCU is not ready for
this.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Paul E. McKenney <paulmck@kernel.org>
Link: https://lore.kernel.org/r/20200521202117.089709607@linutronix.de
There will likely be exception handlers that can sleep, which rules
out the usual approach of invoking rcu_nmi_enter() on entry and also
rcu_nmi_exit() on all exit paths. However, the alternative approach of
just not calling anything can prevent RCU from coaxing quiescent states
from nohz_full CPUs that are looping in the kernel: RCU must instead
IPI them explicitly. It would be better to enable the scheduler tick
on such CPUs to interact with RCU in a lighter-weight manner, and this
enabling is one of the things that rcu_nmi_enter() currently does.
What is needed is something that helps RCU coax quiescent states while
not preventing subsequent sleeps. This commit therefore splits out the
nohz_full scheduler-tick enabling from the rest of the rcu_nmi_enter()
logic into a new function named rcu_irq_enter_check_tick().
[ tglx: Renamed the function and made it a nop when context tracking is off ]
[ mingo: Fixed a CONFIG_NO_HZ_FULL assumption, harmonized and fixed all the
comment blocks and cleaned up rcu_nmi_enter()/exit() definitions. ]
Suggested-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200521202116.996113173@linutronix.de
Same as rcu_is_watching() but without the preempt_disable/enable() pair
inside the function. It is merked noinstr so it ends up in the
non-instrumentable text section.
This is useful for non-preemptible code especially in the low level entry
section. Using rcu_is_watching() there results in a call to the
preempt_schedule_notrace() thunk which triggers noinstr section warnings in
objtool.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200512213810.518709291@linutronix.de
Interrupts and exceptions invoke rcu_irq_enter() on entry and need to
invoke rcu_irq_exit() before they either return to the interrupted code or
invoke the scheduler due to preemption.
The general assumption is that RCU idle code has to have preemption
disabled so that a return from interrupt cannot schedule. So the return
from interrupt code invokes rcu_irq_exit() and preempt_schedule_irq().
If there is any imbalance in the rcu_irq/nmi* invocations or RCU idle code
had preemption enabled then this goes unnoticed until the CPU goes idle or
some other RCU check is executed.
Provide rcu_irq_exit_preempt() which can be invoked from the
interrupt/exception return code in case that preemption is enabled. It
invokes rcu_irq_exit() and contains a few sanity checks in case that
CONFIG_PROVE_RCU is enabled to catch such issues directly.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200505134904.364456424@linutronix.de
The rcu_nmi_enter_common() and rcu_nmi_exit_common() functions take an
"irq" parameter that indicates whether these functions have been invoked from
an irq handler (irq==true) or an NMI handler (irq==false).
However, recent changes have applied notrace to a few critical functions
such that rcu_nmi_enter_common() and rcu_nmi_exit_common() many now rely on
in_nmi(). Note that in_nmi() works no differently than before, but rather
that tracing is now prohibited in code regions where in_nmi() would
incorrectly report NMI state.
Therefore remove the "irq" parameter and inline rcu_nmi_enter_common() and
rcu_nmi_exit_common() into rcu_nmi_enter() and rcu_nmi_exit(),
respectively.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Link: https://lkml.kernel.org/r/20200505134101.617130349@linutronix.de
These functions are invoked from context tracking and other places in the
low level entry code. Move them into the .noinstr.text section to exclude
them from instrumentation.
Mark the places which are safe to invoke traceable functions with
instrumentation_begin/end() so objtool won't complain.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Link: https://lkml.kernel.org/r/20200505134100.575356107@linutronix.de
With earlier commits, the API no longer discards the const-ness of the
sysrq_key_op. As such we can add the notation.
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.com>
Cc: linux-kernel@vger.kernel.org
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: rcu@vger.kernel.org
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Link: https://lore.kernel.org/r/20200513214351.2138580-11-emil.l.velikov@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
fixes.2020.04.27a: Miscellaneous fixes.
kfree_rcu.2020.04.27a: Changes related to kfree_rcu().
rcu-tasks.2020.04.27a: Addition of new RCU-tasks flavors.
stall.2020.04.27a: RCU CPU stall-warning updates.
torture.2020.05.07a: Torture-test updates.
This commit converts three ULONG_CMP_LT() invocations in rcutorture to
time_before() to reflect the fact that they are comparing timestamps to
the jiffies counter.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit fixes the following sparse warning:
kernel/rcu/rcutorture.c:1695:16: warning: symbol 'rcu_fwds' was not declared. Should it be static?
kernel/rcu/rcutorture.c:1696:6: warning: symbol 'rcu_fwd_emergency_stop' was not declared. Should it be static?
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit provides an rcutorture.stall_gp_kthread module parameter
to allow rcutorture to starve the grace-period kthread. This allows
testing the code that detects such starvation.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit aids testing of RCU task stall warning messages by adding
an rcutorture.stall_cpu_block module parameter that results in the
induced stall sleeping within the RCU read-side critical section.
Spinning with interrupts disabled is still available via the
rcutorture.stall_cpu_irqsoff module parameter, and specifying neither
of these two module parameters will spin with preemption disabled.
Note that sleeping (as opposed to preemption) results in additional
complaints from RCU at context-switch time, so yet more testing.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The n_barrier_successes, n_barrier_attempts, and
n_rcu_torture_barrier_error variables are updated (without access
markings) by the main rcu_barrier() test kthread, and accessed (also
without access markings) by the rcu_torture_stats() kthread. This of
course can result in KCSAN complaints.
Because the accesses are in diagnostic prints, this commit uses
data_race() to excuse the diagnostic prints from the data race. If this
were to ever cause bogus statistics prints (for example, due to store
tearing), any misleading information would be disambiguated by the
presence or absence of an rcutorture splat.
This data race was reported by KCSAN. Not appropriate for backporting
due to failure being unlikely and due to the mild consequences of the
failure, namely a confusing rcutorture console message.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
This commit adds stubs for KCSAN's data_race(), ASSERT_EXCLUSIVE_WRITER(),
and ASSERT_EXCLUSIVE_ACCESS() macros to allow code using these macros to
move ahead.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
When all quiescent states have been seen, it is normally the grace-period
kthread that is in trouble. Although the existing stack trace from
the current CPU might possibly provide useful information, experience
indicates that there is too much noise for this to be worthwhile.
This commit therefore removes this stack trace from the output.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
If the grace-period kthread is starved, idle threads' extended quiescent
states are not reported. These idle threads thus wrongly appear to
be blocking the current grace period. This commit therefore tags such
idle threads as probable false positives when the grace-period kthread
is being starved.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Although the accesses used to determine whether or not an expedited
stall should be printed are an integral part of the concurrency algorithm
governing use of the corresponding variables, the values that are simply
printed are ancillary. As such, it is best to use data_race() for these
accesses in order to provide the greatest latitude in the use of KCSAN
for the other accesses that are an integral part of the algorithm. This
commit therefore changes the relevant uses of READ_ONCE() to data_race().
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit allows TASKS_TRACE_RCU to be used independently of TASKS_RCU
and vice versa.
[ paulmck: Fix conditional compilation per kbuild test robot feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit adds a failure-return count for smp_call_function_single(),
and adds this to the console messages for rcutorture writer stalls and at
the end of rcutorture testing.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit adds a counter for the number of times the quiescent state
was an idle task associated with an offline CPU, and prints this count
at the end of rcutorture runs and at stall time.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit adds counts of the number of calls and number of successful
calls to rcu_dynticks_zero_in_eqs(), which are printed at the end
of rcutorture runs and at stall time. This allows evaluation of the
effectiveness of rcu_dynticks_zero_in_eqs().
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit scans the CPUs, adding each CPU's idle task to the list of
tasks that need quiescent states.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The idle task corresponding to an offline CPU can appear to be running
while that CPU is offline. This commit therefore adds checks for this
situation, treating it as a quiescent state. Because the tasklist scan
and the holdout-list scan now exclude CPU-hotplug operations, readers
on the CPU-hotplug paths are still waited for.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit disables CPU hotplug across RCU tasks trace scans, which
is a first step towards correctly recognizing idle tasks "running" on
offline CPUs.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The rcu_read_unlock_trace() can invoke rcu_read_unlock_trace_special(),
which in turn can call wake_up(). Therefore, if any scheduler lock is
held across a call to rcu_read_unlock_trace(), self-deadlock can occur.
This commit therefore uses the irq_work facility to defer the wake_up()
to a clean environment where no scheduler locks will be held.
Reported-by: Steven Rostedt <rostedt@goodmis.org>
[ paulmck: Update #includes for m68k per kbuild test robot. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Systems running CPU-bound real-time task do not want IPIs sent to CPUs
executing nohz_full userspace tasks. Battery-powered systems don't
want IPIs sent to idle CPUs in low-power mode. Unfortunately, RCU tasks
trace can and will send such IPIs in some cases.
Both of these situations occur only when the target CPU is in RCU
dyntick-idle mode, in other words, when RCU is not watching the
target CPU. This suggests that CPUs in dyntick-idle mode should use
memory barriers in outermost invocations of rcu_read_lock_trace()
and rcu_read_unlock_trace(), which would allow the RCU tasks trace
grace period to directly read out the target CPU's read-side state.
One challenge is that RCU tasks trace is not targeting a specific
CPU, but rather a task. And that task could switch from one CPU to
another at any time.
This commit therefore uses try_invoke_on_locked_down_task()
and checks for task_curr() in trc_inspect_reader_notrunning().
When this condition holds, the target task is running and cannot move.
If CONFIG_TASKS_TRACE_RCU_READ_MB=y, the new rcu_dynticks_zero_in_eqs()
function can be used to check if the specified integer (in this case,
t->trc_reader_nesting) is zero while the target CPU remains in that same
dyntick-idle sojourn. If so, the target task is in a quiescent state.
If not, trc_read_check_handler() must indicate failure so that the
grace-period kthread can take appropriate action or retry after an
appropriate delay, as the case may be.
With this change, given CONFIG_TASKS_TRACE_RCU_READ_MB=y, if a given
CPU remains idle or a given task continues executing in nohz_full mode,
the RCU tasks trace grace-period kthread will detect this without the
need to send an IPI.
Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit provides a new TASKS_TRACE_RCU_READ_MB Kconfig option that
enables use of read-side memory barriers by both rcu_read_lock_trace()
and rcu_read_unlock_trace() when the are executed with the
current->trc_reader_special.b.need_mb flag set. This flag is currently
never set. Doing that is the subject of a later commit.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit adds a grace-period count and a count of IPIs sent since
boot, which is printed in response to rcutorture writer stalls and at
the end of rcutorture testing. These counts will be used to evaluate
various schemes to reduce the number of IPIs sent.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit splits ->trc_reader_need_end by using the rcu_special union.
This change permits readers to check to see if a memory barrier is
required without any added overhead in the common case where no such
barrier is required. This commit also adds the read-side checking.
Later commits will add the machinery to properly set the new
->trc_reader_special.b.need_mb field.
This commit also makes rcu_read_unlock_trace_special() tolerate nested
read-side critical sections within interrupt and NMI handlers.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit provides a rcupdate.rcu_task_ipi_delay kernel boot parameter
that specifies how old the RCU tasks trace grace period must be before
the grace-period kthread starts sending IPIs. This delay allows more
tasks to pass through rcu_tasks_qs() quiescent states, thus reducing
(or even eliminating) the number of IPIs that must be sent.
On a short rcutorture test setting this kernel boot parameter to HZ/2
resulted in zero IPIs for all 877 RCU-tasks trace grace periods that
elapsed during that test.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit adds a place to record the grace-period start in jiffies.
This will be used by later commits for debugging purposes and to throttle
IPIs early in the grace period.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit makes the calls to rcu_tasks_qs() detect and report
quiescent states for RCU tasks trace. If the task is in a quiescent
state and if ->trc_reader_checked is not yet set, the task sets its own
->trc_reader_checked. This will cause the grace-period kthread to
remove it from the holdout list if it still remains there.
[ paulmck: Fix conditional compilation per kbuild test robot feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit adds state for each RCU-tasks flavor to the rcutorture
writer stall output. The initial state is minimal, but you have to
start somewhere.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
[ paulmck: Fixes based on feedback from kbuild test robot. ]
This commit pushes the #ifdef CONFIG_TASKS_RCU_GENERIC from
kernel/rcu/update.c to kernel/rcu/tasks.h in order to improve
readability as more APIs are added.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit adds RCU CPU stall warnings for RCU Tasks Trace. These
dump out any tasks blocking the current grace period, as well as any
CPUs that have not responded to an IPI request. This happens in two
phases, when initially extracting state from the tasks and later when
waiting for any holdout tasks to check in.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Because RCU does not watch exception early-entry/late-exit, idle-loop,
or CPU-hotplug execution, protection of tracing and BPF operations is
needlessly complicated. This commit therefore adds a variant of
Tasks RCU that:
o Has explicit read-side markers to allow finite grace periods in
the face of in-kernel loops for PREEMPT=n builds. These markers
are rcu_read_lock_trace() and rcu_read_unlock_trace().
o Protects code in the idle loop, exception entry/exit, and
CPU-hotplug code paths. In this respect, RCU-tasks trace is
similar to SRCU, but with lighter-weight readers.
o Avoids expensive read-side instruction, having overhead similar
to that of Preemptible RCU.
There are of course downsides:
o The grace-period code can send IPIs to CPUs, even when those
CPUs are in the idle loop or in nohz_full userspace. This is
mitigated by later commits.
o It is necessary to scan the full tasklist, much as for Tasks RCU.
o There is a single callback queue guarded by a single lock,
again, much as for Tasks RCU. However, those early use cases
that request multiple grace periods in quick succession are
expected to do so from a single task, which makes the single
lock almost irrelevant. If needed, multiple callback queues
can be provided using any number of schemes.
Perhaps most important, this variant of RCU does not affect the vanilla
flavors, rcu_preempt and rcu_sched. The fact that RCU Tasks Trace
readers can operate from idle, offline, and exception entry/exit in no
way enables rcu_preempt and rcu_sched readers to do so.
The memory ordering was outlined here:
https://lore.kernel.org/lkml/20200319034030.GX3199@paulmck-ThinkPad-P72/
This effort benefited greatly from off-list discussions of BPF
requirements with Alexei Starovoitov and Andrii Nakryiko. At least
some of the on-list discussions are captured in the Link: tags below.
In addition, KCSAN was quite helpful in finding some early bugs.
Link: https://lore.kernel.org/lkml/20200219150744.428764577@infradead.org/
Link: https://lore.kernel.org/lkml/87mu8p797b.fsf@nanos.tec.linutronix.de/
Link: https://lore.kernel.org/lkml/20200225221305.605144982@linutronix.de/
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Andrii Nakryiko <andriin@fb.com>
[ paulmck: Apply feedback from Steve Rostedt and Joel Fernandes. ]
[ paulmck: Decrement trc_n_readers_need_end upon IPI failure. ]
[ paulmck: Fix locking issue reported by rcutorture. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit refactors RCU tasks to allow variants to be added. These
variants will share the current Tasks-RCU tasklist scan and the holdout
list processing.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit causes the flavors of RCU Tasks to use different names
for their kthreads and in their console messages.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit adds a "rude" variant of RCU-tasks that has as quiescent
states schedule(), cond_resched_tasks_rcu_qs(), userspace execution,
and (in theory, anyway) cond_resched(). In other words, RCU-tasks rude
readers are regions of code with preemption disabled, but excluding code
early in the CPU-online sequence and late in the CPU-offline sequence.
Updates make use of IPIs and force an IPI and a context switch on each
online CPU. This variant is useful in some situations in tracing.
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
[ paulmck: Apply EXPORT_SYMBOL_GPL() feedback from Qiujun Huang. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
[ paulmck: Apply review feedback from Steve Rostedt. ]
This commit splits out generic processing from RCU-tasks-specific
processing in order to allow additional flavors to be added. It also
adds a def_bool TASKS_RCU_GENERIC to enable the common RCU-tasks
infrastructure code.
This is primarily, but not entirely, a code-movement commit.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit adds a crude test for synchronize_rcu_mult(). This is
currently a smoke test rather than a high-quality stress test.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit creates an rcu_tasks struct to hold state information for
RCU Tasks. This is a preparation commit for adding additional flavors
of Tasks RCU, each of which would have its own rcu_tasks struct.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This code-movement-only commit is in preparation for adding an additional
flavor of Tasks RCU, which relies on workqueues to detect grace periods.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Currently, an RCU-preempt CPU stall warning simply lists the PIDs of
those tasks holding up the current grace period. This can be helpful,
but more can be even more helpful.
To this end, this commit adds the nesting level, whether the task
thinks it was preempted in its current RCU read-side critical section,
whether RCU core has asked this task for a quiescent state, whether the
expedited-grace-period hint is set, and whether the task believes that
it is on the blocked-tasks list (it must be, or it would not be printed,
but if things are broken, best not to take too much for granted).
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Currently, the PREEMPT=y version of rcu_note_context_switch() does not
invoke rcu_tasks_qs(), and we need it to in order to keep RCU Tasks
Trace's IPIs down to a dull roar. This commit therefore enables this
hook.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
It is not as clear as it might be just where in RCU's idle entry/exit
code RCU stops and starts watching the current CPU. This commit therefore
adds comments calling out the transitions.
Reported-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Now that it should be safe to hold scheduler locks across
rcu_read_unlock(), even in cases where the corresponding RCU read-side
critical section might have been preempted and boosted, the commit adds
a test of this capability to rcutorture. This has been tested on current
mainline (which can deadlock in this situation), and lockdep duly reported
the expected deadlock. On -rcu, lockdep is silent, thus far, anyway.
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Now that RCU flavors have been consolidated, an RCU-preempt
rcu_read_unlock() in an interrupt or softirq handler cannot possibly
end the RCU read-side critical section. Consider the old vulnerability
involving rcu_read_unlock() being invoked within such a handler that
interrupted an __rcu_read_unlock_special(), in which a wakeup might be
invoked with a scheduler lock held. Because rcu_read_unlock_special()
no longer does wakeups in such situations, it is no longer necessary
for __rcu_read_unlock() to set the nesting level negative.
This commit therefore removes this recursion-protection code from
__rcu_read_unlock().
[ paulmck: Let rcu_exp_handler() continue to call rcu_report_exp_rdp(). ]
[ paulmck: Adjust other checks given no more negative nesting. ]
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The ->rcu_read_unlock_special.b.deferred_qs field is set to true in
rcu_read_unlock_special() but never set to false. This is not
particularly useful, so this commit removes this field.
The only possible justification for this field is to ease debugging
of RCU deferred quiscent states, but the combination of the other
->rcu_read_unlock_special fields plus ->rcu_blocked_node and of course
->rcu_read_lock_nesting should cover debugging needs. And if this last
proves incorrect, this patch can always be reverted, along with the
required setting of ->rcu_read_unlock_special.b.deferred_qs to false
in rcu_preempt_deferred_qs_irqrestore().
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Now that RCU flavors have been consolidated, an RCU-preempt
rcu_read_unlock() in an interrupt or softirq handler cannot possibly
end the RCU read-side critical section. Consider the old vulnerability
involving rcu_preempt_deferred_qs() being invoked within such a handler
that interrupted an extended RCU read-side critical section, in which
a wakeup might be invoked with a scheduler lock held. Because
rcu_read_unlock_special() no longer does wakeups in such situations,
it is no longer necessary for rcu_preempt_deferred_qs() to set the
nesting level negative.
This commit therefore removes this recursion-protection code from
rcu_preempt_deferred_qs().
[ paulmck: Fix typo in commit log per Steve Rostedt. ]
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The scheduler is currently required to hold rq/pi locks across the entire
RCU read-side critical section or not at all. This is inconvenient and
leaves traps for the unwary, including the author of this commit.
But now that excessively long grace periods enable scheduling-clock
interrupts for holdout nohz_full CPUs, the nohz_full rescue logic in
rcu_read_unlock_special() can be dispensed with. In other words, the
rcu_read_unlock_special() function can refrain from doing wakeups unless
such wakeups are guaranteed safe.
This commit therefore avoids unsafe wakeups, freeing the scheduler to
hold rq/pi locks across rcu_read_unlock() even if the corresponding RCU
read-side critical section might have been preempted. This commit also
updates RCU's requirements documentation.
This commit is inspired by a patch from Lai Jiangshan:
https://lore.kernel.org/lkml/20191102124559.1135-2-laijs@linux.alibaba.com
This commit is further intended to be a step towards his goal of permitting
the inlining of RCU-preempt's rcu_read_lock() and rcu_read_unlock().
Cc: Lai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit adds stubs for KCSAN's data_race(), ASSERT_EXCLUSIVE_WRITER(),
and ASSERT_EXCLUSIVE_ACCESS() macros to allow code using these macros
to move ahead.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit adds rcu_gp_might_be_stalled(), which returns true if there
is some reason to believe that the RCU grace period is stalled. The use
case is where an RCU free-memory path needs to allocate memory in order
to free it, a situation that should be avoided where possible.
But where it is necessary, there is always the alternative of using
synchronize_rcu() to wait for a grace period in order to avoid the
allocation. And if the grace period is stalled, allocating memory to
asynchronously wait for it is a bad idea of epic proportions: Far better
to let others use the memory, because these others might actually be
able to free that memory before the grace period ends.
Thus, rcu_gp_might_be_stalled() can be used to help decide whether
allocating memory on an RCU free path is a semi-reasonable course
of action.
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Uladzislau Rezki <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
We can relax the correctness of counting of number of queued objects in
favor of not hurting performance, by locklessly sampling per-cpu
counters. This should be Ok since under high memory pressure, it should not
matter if we are off by a few objects while counting. The shrinker will
still do the reclaim.
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
[ paulmck: Remove unused "flags" variable. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
To reduce grace periods and improve kfree() performance, we have done
batching recently dramatically bringing down the number of grace periods
while giving us the ability to use kfree_bulk() for efficient kfree'ing.
However, this has increased the likelihood of OOM condition under heavy
kfree_rcu() flood on small memory systems. This patch introduces a
shrinker which starts grace periods right away if the system is under
memory pressure due to existence of objects that have still not started
a grace period.
With this patch, I do not observe an OOM anymore on a system with 512MB
RAM and 8 CPUs, with the following rcuperf options:
rcuperf.kfree_loops=20000 rcuperf.kfree_alloc_num=8000
rcuperf.kfree_rcu_test=1 rcuperf.kfree_mult=2
Otherwise it easily OOMs with the above parameters.
NOTE:
1. On systems with no memory pressure, the patch has no effect as intended.
2. In the future, we can use this same mechanism to prevent grace periods
from happening even more, by relying on shrinkers carefully.
Cc: urezki@gmail.com
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This allows us to increase memory pressure dynamically using a new
rcuperf boot command line parameter called 'rcumult'.
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit converts the ULONG_CMP_LT() in rcu_nohz_full_cpu() to
time_before() to reflect the fact that it is comparing a timestamp to
the jiffies counter.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit converts the ULONG_CMP_GE() in rcu_initiate_boost() to
time_after() to reflect the fact that it is comparing a timestamp to
the jiffies counter.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit converts the ULONG_CMP_GE() in rcu_gp_fqs_loop() to
time_after() to reflect the fact that it is comparing a timestamp to
the jiffies counter.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Coccinelle reports a warning at use_softirq declaration
WARNING: Assignment of 0/1 to bool variable
The root cause is
use_softirq a variable of bool type is initialised with the integer 1
Replacing 1 with value true solve the issue.
Signed-off-by: Jules Irenge <jbi.octave@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Coccinelle reports warnings at rcu_read_lock_held_common()
WARNING: Assignment of 0/1 to bool variable
To fix this,
the assigned pointer ret values are replaced by corresponding boolean value.
Given that ret is a pointer of bool type
Signed-off-by: Jules Irenge <jbi.octave@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The rcu_state structure's gp_seq field is only to be modified by the RCU
grace-period kthread, which is single-threaded. This commit therefore
enlists KCSAN's help in enforcing this restriction. This commit applies
KCSAN-specific primitives, so cannot go upstream until KCSAN does.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit escapes *ret, because otherwise the documentation system
thinks that this is an incomplete emphasis block:
./kernel/rcu/update.c:65: WARNING: Inline emphasis start-string without end-string.
./kernel/rcu/update.c:65: WARNING: Inline emphasis start-string without end-string.
./kernel/rcu/update.c:70: WARNING: Inline emphasis start-string without end-string.
./kernel/rcu/update.c:82: WARNING: Inline emphasis start-string without end-string.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
