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workqueue: defer the worker wakeup outside pool->lock in process_one_work()

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Use kick_pool_pick() to select and claim the worker under pool->lock and
issue the wakeup with wake_up_process() after the lock is dropped.

Unlike __queue_work(), this path has no surrounding RCU section, so take
rcu_read_lock() before dropping pool->lock to keep the picked worker's
task_struct valid across the wakeup.

Signed-off-by: Breno Leitao <leitao@debian.org>
Tested-by: Krishna Magar <kmagar@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Breno Leitao 2026-06-26 02:57:55 -07:00 committed by Tejun Heo
parent d070f2916a
commit f504706a25
1 changed files with 10 additions and 1 deletions
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11
kernel/workqueue.c
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@ -3251,6 +3251,7 @@ __acquires(&pool->lock)
{
struct pool_workqueue *pwq = get_work_pwq(work);
struct worker_pool *pool = worker->pool;
struct task_struct *wake_task = NULL;
unsigned long work_data;
int lockdep_start_depth, rcu_start_depth;
bool bh_draining = pool->flags & POOL_BH_DRAINING;
@ -3304,8 +3305,11 @@ __acquires(&pool->lock)
* since nr_running would always be >= 1 at this point. This is used to
* chain execution of the pending work items for WORKER_NOT_RUNNING
* workers such as the UNBOUND and CPU_INTENSIVE ones.
*
* Select the worker under pool->lock; the wakeup is deferred until
* after the lock is dropped, guarded by the rcu_read_lock() below.
*/
kick_pool(pool);
kick_pool_pick(pool, &wake_task);
/*
* Record the last pool and clear PENDING which should be the last
@ -3316,7 +3320,12 @@ __acquires(&pool->lock)
set_work_pool_and_clear_pending(work, pool->id, pool_offq_flags(pool));
pwq->stats[PWQ_STAT_STARTED]++;
rcu_read_lock();
raw_spin_unlock_irq(&pool->lock);
if (wake_task)
wake_up_process(wake_task);
rcu_read_unlock();
rcu_start_depth = rcu_preempt_depth();
lockdep_start_depth = lockdep_depth(current);