diff options
author | Frederic Weisbecker <frederic@kernel.org> | 2023-09-24 18:07:02 +0300 |
---|---|---|
committer | Tejun Heo <tj@kernel.org> | 2023-10-18 12:49:19 +0300 |
commit | 265f3ed077036f053981f5eea0b5b43e7c5b39ff (patch) | |
tree | c8f45b8c326f337bb7b578b24d80ae5dfa3d8ad9 /kernel/workqueue.c | |
parent | 06dc10eae55b5ceabfef287a7e5f16ceea204aa0 (diff) | |
download | linux-265f3ed077036f053981f5eea0b5b43e7c5b39ff.tar.xz |
workqueue: Provide one lock class key per work_on_cpu() callsite
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>
Diffstat (limited to 'kernel/workqueue.c')
-rw-r--r-- | kernel/workqueue.c | 20 |
1 files changed, 12 insertions, 8 deletions
diff --git a/kernel/workqueue.c b/kernel/workqueue.c index a3522b70218d..0f682da96e1c 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -5622,50 +5622,54 @@ static void work_for_cpu_fn(struct work_struct *work) } /** - * work_on_cpu - run a function in thread context on a particular cpu + * work_on_cpu_key - run a function in thread context on a particular cpu * @cpu: the cpu to run on * @fn: the function to run * @arg: the function arg + * @key: The lock class key for lock debugging purposes * * It is up to the caller to ensure that the cpu doesn't go offline. * The caller must not hold any locks which would prevent @fn from completing. * * Return: The value @fn returns. */ -long work_on_cpu(int cpu, long (*fn)(void *), void *arg) +long work_on_cpu_key(int cpu, long (*fn)(void *), + void *arg, struct lock_class_key *key) { struct work_for_cpu wfc = { .fn = fn, .arg = arg }; - INIT_WORK_ONSTACK(&wfc.work, work_for_cpu_fn); + INIT_WORK_ONSTACK_KEY(&wfc.work, work_for_cpu_fn, key); schedule_work_on(cpu, &wfc.work); flush_work(&wfc.work); destroy_work_on_stack(&wfc.work); return wfc.ret; } -EXPORT_SYMBOL_GPL(work_on_cpu); +EXPORT_SYMBOL_GPL(work_on_cpu_key); /** - * work_on_cpu_safe - run a function in thread context on a particular cpu + * work_on_cpu_safe_key - run a function in thread context on a particular cpu * @cpu: the cpu to run on * @fn: the function to run * @arg: the function argument + * @key: The lock class key for lock debugging purposes * * Disables CPU hotplug and calls work_on_cpu(). The caller must not hold * any locks which would prevent @fn from completing. * * Return: The value @fn returns. */ -long work_on_cpu_safe(int cpu, long (*fn)(void *), void *arg) +long work_on_cpu_safe_key(int cpu, long (*fn)(void *), + void *arg, struct lock_class_key *key) { long ret = -ENODEV; cpus_read_lock(); if (cpu_online(cpu)) - ret = work_on_cpu(cpu, fn, arg); + ret = work_on_cpu_key(cpu, fn, arg, key); cpus_read_unlock(); return ret; } -EXPORT_SYMBOL_GPL(work_on_cpu_safe); +EXPORT_SYMBOL_GPL(work_on_cpu_safe_key); #endif /* CONFIG_SMP */ #ifdef CONFIG_FREEZER |