[ Upstream commit 265f3ed077036f053981f5eea0b5b43e7c5b39ff ]
All callers of work_on_cpu() share the same lock class key for all the
functions queued. As a result the workqueue related locking scenario for
a function A may be spuriously accounted as an inversion against the
locking scenario of function B such as in the following model:
long A(void *arg)
{
mutex_lock(&mutex);
mutex_unlock(&mutex);
}
long B(void *arg)
{
}
void launchA(void)
{
work_on_cpu(0, A, NULL);
}
void launchB(void)
{
mutex_lock(&mutex);
work_on_cpu(1, B, NULL);
mutex_unlock(&mutex);
}
launchA and launchB running concurrently have no chance to deadlock.
However the above can be reported by lockdep as a possible locking
inversion because the works containing A() and B() are treated as
belonging to the same locking class.
The following shows an existing example of such a spurious lockdep splat:
======================================================
WARNING: possible circular locking dependency detected
6.6.0-rc1-00065-g934ebd6e5359 #35409 Not tainted
------------------------------------------------------
kworker/0:1/9 is trying to acquire lock:
ffffffff9bc72f30 (cpu_hotplug_lock){++++}-{0:0}, at: _cpu_down+0x57/0x2b0
but task is already holding lock:
ffff9e3bc0057e60 ((work_completion)(&wfc.work)){+.+.}-{0:0}, at: process_scheduled_works+0x216/0x500
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #2 ((work_completion)(&wfc.work)){+.+.}-{0:0}:
__flush_work+0x83/0x4e0
work_on_cpu+0x97/0xc0
rcu_nocb_cpu_offload+0x62/0xb0
rcu_nocb_toggle+0xd0/0x1d0
kthread+0xe6/0x120
ret_from_fork+0x2f/0x40
ret_from_fork_asm+0x1b/0x30
-> #1 (rcu_state.barrier_mutex){+.+.}-{3:3}:
__mutex_lock+0x81/0xc80
rcu_nocb_cpu_deoffload+0x38/0xb0
rcu_nocb_toggle+0x144/0x1d0
kthread+0xe6/0x120
ret_from_fork+0x2f/0x40
ret_from_fork_asm+0x1b/0x30
-> #0 (cpu_hotplug_lock){++++}-{0:0}:
__lock_acquire+0x1538/0x2500
lock_acquire+0xbf/0x2a0
percpu_down_write+0x31/0x200
_cpu_down+0x57/0x2b0
__cpu_down_maps_locked+0x10/0x20
work_for_cpu_fn+0x15/0x20
process_scheduled_works+0x2a7/0x500
worker_thread+0x173/0x330
kthread+0xe6/0x120
ret_from_fork+0x2f/0x40
ret_from_fork_asm+0x1b/0x30
other info that might help us debug this:
Chain exists of:
cpu_hotplug_lock --> rcu_state.barrier_mutex --> (work_completion)(&wfc.work)
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock((work_completion)(&wfc.work));
lock(rcu_state.barrier_mutex);
lock((work_completion)(&wfc.work));
lock(cpu_hotplug_lock);
*** DEADLOCK ***
2 locks held by kworker/0:1/9:
#0: ffff900481068b38 ((wq_completion)events){+.+.}-{0:0}, at: process_scheduled_works+0x212/0x500
#1: ffff9e3bc0057e60 ((work_completion)(&wfc.work)){+.+.}-{0:0}, at: process_scheduled_works+0x216/0x500
stack backtrace:
CPU: 0 PID: 9 Comm: kworker/0:1 Not tainted 6.6.0-rc1-00065-g934ebd6e5359 #35409
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014
Workqueue: events work_for_cpu_fn
Call Trace:
rcu-torture: rcu_torture_read_exit: Start of episode
<TASK>
dump_stack_lvl+0x4a/0x80
check_noncircular+0x132/0x150
__lock_acquire+0x1538/0x2500
lock_acquire+0xbf/0x2a0
? _cpu_down+0x57/0x2b0
percpu_down_write+0x31/0x200
? _cpu_down+0x57/0x2b0
_cpu_down+0x57/0x2b0
__cpu_down_maps_locked+0x10/0x20
work_for_cpu_fn+0x15/0x20
process_scheduled_works+0x2a7/0x500
worker_thread+0x173/0x330
? __pfx_worker_thread+0x10/0x10
kthread+0xe6/0x120
? __pfx_kthread+0x10/0x10
ret_from_fork+0x2f/0x40
? __pfx_kthread+0x10/0x10
ret_from_fork_asm+0x1b/0x30
</TASK
Fix this with providing one lock class key per work_on_cpu() caller.
Reported-and-tested-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
[ Upstream commit ca10d851b9ad0338c19e8e3089e24d565ebfffd7 ]
Commit 5c0338c68706 ("workqueue: restore WQ_UNBOUND/max_active==1
to be ordered") enabled implicit ordered attribute to be added to
WQ_UNBOUND workqueues with max_active of 1. This prevented the changing
of attributes to these workqueues leading to fix commit 0a94efb5acbb
("workqueue: implicit ordered attribute should be overridable").
However, workqueue_apply_unbound_cpumask() was not updated at that time.
So sysfs changes to wq_unbound_cpumask has no effect on WQ_UNBOUND
workqueues with implicit ordered attribute. Since not all WQ_UNBOUND
workqueues are visible on sysfs, we are not able to make all the
necessary cpumask changes even if we iterates all the workqueue cpumasks
in sysfs and changing them one by one.
Fix this problem by applying the corresponding change made
to apply_workqueue_attrs_locked() in the fix commit to
workqueue_apply_unbound_cpumask().
Fixes: 5c0338c68706 ("workqueue: restore WQ_UNBOUND/max_active==1 to be ordered")
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
[ Upstream commit fe48ba7daefe75bbbefa2426deddc05f2d530d2d ]
KCSAN has discovered a data race in kernel/workqueue.c:2598:
[ 1863.554079] ==================================================================
[ 1863.554118] BUG: KCSAN: data-race in process_one_work / process_one_work
[ 1863.554142] write to 0xffff963d99d79998 of 8 bytes by task 5394 on cpu 27:
[ 1863.554154] process_one_work (kernel/workqueue.c:2598)
[ 1863.554166] worker_thread (./include/linux/list.h:292 kernel/workqueue.c:2752)
[ 1863.554177] kthread (kernel/kthread.c:389)
[ 1863.554186] ret_from_fork (arch/x86/kernel/process.c:145)
[ 1863.554197] ret_from_fork_asm (arch/x86/entry/entry_64.S:312)
[ 1863.554213] read to 0xffff963d99d79998 of 8 bytes by task 5450 on cpu 12:
[ 1863.554224] process_one_work (kernel/workqueue.c:2598)
[ 1863.554235] worker_thread (./include/linux/list.h:292 kernel/workqueue.c:2752)
[ 1863.554247] kthread (kernel/kthread.c:389)
[ 1863.554255] ret_from_fork (arch/x86/kernel/process.c:145)
[ 1863.554266] ret_from_fork_asm (arch/x86/entry/entry_64.S:312)
[ 1863.554280] value changed: 0x0000000000001766 -> 0x000000000000176a
[ 1863.554295] Reported by Kernel Concurrency Sanitizer on:
[ 1863.554303] CPU: 12 PID: 5450 Comm: kworker/u64:1 Tainted: G L 6.5.0-rc6+ #44
[ 1863.554314] Hardware name: ASRock X670E PG Lightning/X670E PG Lightning, BIOS 1.21 04/26/2023
[ 1863.554322] Workqueue: btrfs-endio btrfs_end_bio_work [btrfs]
[ 1863.554941] ==================================================================
lockdep_invariant_state(true);
→ pwq->stats[PWQ_STAT_STARTED]++;
trace_workqueue_execute_start(work);
worker->current_func(work);
Moving pwq->stats[PWQ_STAT_STARTED]++; before the line
raw_spin_unlock_irq(&pool->lock);
resolves the data race without performance penalty.
KCSAN detected at least one additional data race:
[ 157.834751] ==================================================================
[ 157.834770] BUG: KCSAN: data-race in process_one_work / process_one_work
[ 157.834793] write to 0xffff9934453f77a0 of 8 bytes by task 468 on cpu 29:
[ 157.834804] process_one_work (/home/marvin/linux/kernel/linux_torvalds/kernel/workqueue.c:2606)
[ 157.834815] worker_thread (/home/marvin/linux/kernel/linux_torvalds/./include/linux/list.h:292 /home/marvin/linux/kernel/linux_torvalds/kernel/workqueue.c:2752)
[ 157.834826] kthread (/home/marvin/linux/kernel/linux_torvalds/kernel/kthread.c:389)
[ 157.834834] ret_from_fork (/home/marvin/linux/kernel/linux_torvalds/arch/x86/kernel/process.c:145)
[ 157.834845] ret_from_fork_asm (/home/marvin/linux/kernel/linux_torvalds/arch/x86/entry/entry_64.S:312)
[ 157.834859] read to 0xffff9934453f77a0 of 8 bytes by task 214 on cpu 7:
[ 157.834868] process_one_work (/home/marvin/linux/kernel/linux_torvalds/kernel/workqueue.c:2606)
[ 157.834879] worker_thread (/home/marvin/linux/kernel/linux_torvalds/./include/linux/list.h:292 /home/marvin/linux/kernel/linux_torvalds/kernel/workqueue.c:2752)
[ 157.834890] kthread (/home/marvin/linux/kernel/linux_torvalds/kernel/kthread.c:389)
[ 157.834897] ret_from_fork (/home/marvin/linux/kernel/linux_torvalds/arch/x86/kernel/process.c:145)
[ 157.834907] ret_from_fork_asm (/home/marvin/linux/kernel/linux_torvalds/arch/x86/entry/entry_64.S:312)
[ 157.834920] value changed: 0x000000000000052a -> 0x0000000000000532
[ 157.834933] Reported by Kernel Concurrency Sanitizer on:
[ 157.834941] CPU: 7 PID: 214 Comm: kworker/u64:2 Tainted: G L 6.5.0-rc7-kcsan-00169-g81eaf55a60fc #4
[ 157.834951] Hardware name: ASRock X670E PG Lightning/X670E PG Lightning, BIOS 1.21 04/26/2023
[ 157.834958] Workqueue: btrfs-endio btrfs_end_bio_work [btrfs]
[ 157.835567] ==================================================================
in code:
trace_workqueue_execute_end(work, worker->current_func);
→ pwq->stats[PWQ_STAT_COMPLETED]++;
lock_map_release(&lockdep_map);
lock_map_release(&pwq->wq->lockdep_map);
which needs to be resolved separately.
Fixes: 725e8ec59c56c ("workqueue: Add pwq->stats[] and a monitoring script")
Cc: Tejun Heo <tj@kernel.org>
Suggested-by: Lai Jiangshan <jiangshanlai@gmail.com>
Link: https://lore.kernel.org/lkml/20230818194448.29672-1-mirsad.todorovac@alu.unizg.hr/
Signed-off-by: Mirsad Goran Todorovac <mirsad.todorovac@alu.unizg.hr>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
wq_cpu_intensive_thresh_us is used to detect CPU-hogging per-cpu work items. Once detected, they're excluded from concurrency management to prevent them from blocking other per-cpu work items. If CONFIG_WQ_CPU_INTENSIVE_REPORT is enabled, repeat offenders are also reported so that the code can be updated. The default threshold is 10ms which is long enough to do fair bit of work on modern CPUs while short enough to be usually not noticeable. This unfortunately leads to a lot of, arguable spurious, detections on very slow CPUs. Using the same threshold across CPUs whose performance levels may be apart by multiple levels of magnitude doesn't make whole lot of sense. This patch scales up wq_cpu_intensive_thresh_us upto 1 second when BogoMIPS is below 4000. This is obviously very inaccurate but it doesn't have to be accurate to be useful. The mechanism is still useful when the threshold is fully scaled up and the benefits of reports are usually shared with everyone regardless of who's reporting, so as long as there are sufficient number of fast machines reporting, we don't lose much. Some (or is it all?) ARM CPUs systemtically report significantly lower BogoMIPS. While this doesn't break anything, given how widespread ARM CPUs are, it's at least a missed opportunity and it probably would be a good idea to teach workqueue about it. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-and-Tested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Pull workqueue updates from Tejun Heo: - Concurrency-managed per-cpu work items that hog CPUs and delay the execution of other work items are now automatically detected and excluded from concurrency management. Reporting on such work items can also be enabled through a config option. - Added tools/workqueue/wq_monitor.py which improves visibility into workqueue usages and behaviors. - Arnd's minimal fix for gcc-13 enum warning on 32bit compiles, superseded by commit afa4bb778e48 in mainline. * tag 'wq-for-6.5' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq: workqueue: Disable per-cpu CPU hog detection when wq_cpu_intensive_thresh_us is 0 workqueue: Fix WARN_ON_ONCE() triggers in worker_enter_idle() workqueue: fix enum type for gcc-13 workqueue: Track and monitor per-workqueue CPU time usage workqueue: Report work funcs that trigger automatic CPU_INTENSIVE mechanism workqueue: Automatically mark CPU-hogging work items CPU_INTENSIVE workqueue: Improve locking rule description for worker fields workqueue: Move worker_set/clr_flags() upwards workqueue: Re-order struct worker fields workqueue: Add pwq->stats[] and a monitoring script Further upgrade queue_work_on() comment
Dave Airlie reports that gcc-13.1.1 has started complaining about some
of the workqueue code in 32-bit arm builds:
kernel/workqueue.c: In function ‘get_work_pwq’:
kernel/workqueue.c:713:24: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
713 | return (void *)(data & WORK_STRUCT_WQ_DATA_MASK);
| ^
[ ... a couple of other cases ... ]
and while it's not immediately clear exactly why gcc started complaining
about it now, I suspect it's some C23-induced enum type handlign fixup in
gcc-13 is the cause.
Whatever the reason for starting to complain, the code and data types
are indeed disgusting enough that the complaint is warranted.
The wq code ends up creating various "helper constants" (like that
WORK_STRUCT_WQ_DATA_MASK) using an enum type, which is all kinds of
confused. The mask needs to be 'unsigned long', not some unspecified
enum type.
To make matters worse, the actual "mask and cast to a pointer" is
repeated a couple of times, and the cast isn't even always done to the
right pointer, but - as the error case above - to a 'void *' with then
the compiler finishing the job.
That's now how we roll in the kernel.
So create the masks using the proper types rather than some ambiguous
enumeration, and use a nice helper that actually does the type
conversion in one well-defined place.
Incidentally, this magically makes clang generate better code. That,
admittedly, is really just a sign of clang having been seriously
confused before, and cleaning up the typing unconfuses the compiler too.
Reported-by: Dave Airlie <airlied@gmail.com>
Link: https://lore.kernel.org/lkml/CAPM=9twNnV4zMCvrPkw3H-ajZOH-01JVh_kDrxdPYQErz8ZTdA@mail.gmail.com/
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Tejun Heo <tj@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
If workqueue.cpu_intensive_thresh_us is set to 0, the detection mechanism
for CPU-hogging per-cpu work item will keep triggering spuriously:
workqueue: process_srcu hogged CPU for >0us 4 times, consider switching to WQ_UNBOUND
workqueue: gc_worker hogged CPU for >0us 4 times, consider switching to WQ_UNBOUND
workqueue: gc_worker hogged CPU for >0us 8 times, consider switching to WQ_UNBOUND
workqueue: wait_rcu_exp_gp hogged CPU for >0us 4 times, consider switching to WQ_UNBOUND
workqueue: kfree_rcu_monitor hogged CPU for >0us 4 times, consider switching to WQ_UNBOUND
workqueue: kfree_rcu_monitor hogged CPU for >0us 8 times, consider switching to WQ_UNBOUND
workqueue: reg_todo hogged CPU for >0us 4 times, consider switching to WQ_UNBOUND
This commit therefore disables the CPU-hog detection mechanism when
workqueue.cpu_intensive_thresh_us is set to 0.
tj: Patch description updated and the condition check on
cpu_intensive_thresh_us separated into a separate if statement for
readability.
Signed-off-by: Zqiang <qiang.zhang1211@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Currently, pool->nr_running can be modified from timer tick, that means the
timer tick can run nested inside a not-irq-protected section that's in the
process of modifying nr_running. Consider the following scenario:
CPU0
kworker/0:2 (events)
worker_clr_flags(worker, WORKER_PREP | WORKER_REBOUND);
->pool->nr_running++; (1)
process_one_work()
->worker->current_func(work);
->schedule()
->wq_worker_sleeping()
->worker->sleeping = 1;
->pool->nr_running--; (0)
....
->wq_worker_running()
....
CPU0 by interrupt:
wq_worker_tick()
->worker_set_flags(worker, WORKER_CPU_INTENSIVE);
->pool->nr_running--; (-1)
->worker->flags |= WORKER_CPU_INTENSIVE;
....
->if (!(worker->flags & WORKER_NOT_RUNNING))
->pool->nr_running++; (will not execute)
->worker->sleeping = 0;
....
->worker_clr_flags(worker, WORKER_CPU_INTENSIVE);
->pool->nr_running++; (0)
....
worker_set_flags(worker, WORKER_PREP);
->pool->nr_running--; (-1)
....
worker_enter_idle()
->WARN_ON_ONCE(pool->nr_workers == pool->nr_idle && pool->nr_running);
if the nr_workers is equal to nr_idle, due to the nr_running is not zero,
will trigger WARN_ON_ONCE().
[ 2.460602] WARNING: CPU: 0 PID: 63 at kernel/workqueue.c:1999 worker_enter_idle+0xb2/0xc0
[ 2.462163] Modules linked in:
[ 2.463401] CPU: 0 PID: 63 Comm: kworker/0:2 Not tainted 6.4.0-rc2-next-20230519 #1
[ 2.463771] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-2 04/01/2014
[ 2.465127] Workqueue: 0x0 (events)
[ 2.465678] RIP: 0010:worker_enter_idle+0xb2/0xc0
...
[ 2.472614] Call Trace:
[ 2.473152] <TASK>
[ 2.474182] worker_thread+0x71/0x430
[ 2.474992] ? _raw_spin_unlock_irqrestore+0x28/0x50
[ 2.475263] kthread+0x103/0x120
[ 2.475493] ? __pfx_worker_thread+0x10/0x10
[ 2.476355] ? __pfx_kthread+0x10/0x10
[ 2.476635] ret_from_fork+0x2c/0x50
[ 2.477051] </TASK>
This commit therefore add the check of worker->sleeping in wq_worker_tick(),
if the worker->sleeping is not zero, directly return.
tj: Updated comment and description.
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
Tested-by: Anders Roxell <anders.roxell@linaro.org>
Closes: https://qa-reports.linaro.org/lkft/linux-next-master/build/next-20230519/testrun/17078554/suite/boot/test/clang-nightly-lkftconfig/log
Signed-off-by: Zqiang <qiang.zhang1211@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Now that wq_worker_tick() is there, we can easily track the rough CPU time
consumption of each workqueue by charging the whole tick whenever a tick
hits an active workqueue. While not super accurate, it provides reasonable
visibility into the workqueues that consume a lot of CPU cycles.
wq_monitor.py is updated to report the per-workqueue CPU times.
v2: wq_monitor.py was using "cputime" as the key when outputting in json
format. Use "cpu_time" instead for consistency with other fields.
Signed-off-by: Tejun Heo <tj@kernel.org>
Workqueue now automatically marks per-cpu work items that hog CPU for too
long as CPU_INTENSIVE, which excludes them from concurrency management and
prevents stalling other concurrency-managed work items. If a work function
keeps running over the thershold, it likely needs to be switched to use an
unbound workqueue.
This patch adds a debug mechanism which tracks the work functions which
trigger the automatic CPU_INTENSIVE mechanism and report them using
pr_warn() with exponential backoff.
v3: Documentation update.
v2: Drop bouncing to kthread_worker for printing messages. It was to avoid
introducing circular locking dependency through printk but not effective
as it still had pool lock -> wci_lock -> printk -> pool lock loop. Let's
just print directly using printk_deferred().
Signed-off-by: Tejun Heo <tj@kernel.org>
Suggested-by: Peter Zijlstra <peterz@infradead.org>