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workqueue: Move pwq_dec_nr_in_flight() to the end of work item handling 

The planned shared nr_active handling for unbound workqueues will make
pwq_dec_nr_active() sometimes drop the pool lock temporarily to acquire
other pool locks, which is necessary as retirement of an nr_active count
from one pool may need kick off an inactive work item in another pool.

This patch moves pwq_dec_nr_in_flight() call in try_to_grab_pending() to the
end of work item handling so that work item state changes stay atomic.
process_one_work() which is the other user of pwq_dec_nr_in_flight() already
calls it at the end of work item handling. Comments are added to both call
sites and pwq_dec_nr_in_flight().

This shouldn't cause any behavior changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Lai Jiangshan <jiangshanlai@gmail.com>
This commit is contained in:
Tejun Heo 2024-01-29 08:11:24 -10:00
parent 9f66cff212
commit dd6c3c5441
1 changed files with 10 additions and 1 deletions
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11
kernel/workqueue.c
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@ -1587,6 +1587,11 @@ static void pwq_dec_nr_active(struct pool_workqueue *pwq)
* A work either has completed or is removed from pending queue,
* decrement nr_in_flight of its pwq and handle workqueue flushing.
*
* NOTE:
* For unbound workqueues, this function may temporarily drop @pwq->pool->lock
* and thus should be called after all other state updates for the in-flight
* work item is complete.
*
* CONTEXT:
* raw_spin_lock_irq(pool->lock).
*/
@ -1711,11 +1716,13 @@ static int try_to_grab_pending(struct work_struct *work, bool is_dwork,
pwq_activate_work(pwq, work);
list_del_init(&work->entry);
pwq_dec_nr_in_flight(pwq, *work_data_bits(work));
/* work->data points to pwq iff queued, point to pool */
set_work_pool_and_keep_pending(work, pool->id);
/* must be the last step, see the function comment */
pwq_dec_nr_in_flight(pwq, *work_data_bits(work));
raw_spin_unlock(&pool->lock);
rcu_read_unlock();
return 1;
@ -2780,6 +2787,8 @@ __acquires(&pool->lock)
worker->current_func = NULL;
worker->current_pwq = NULL;
worker->current_color = INT_MAX;
/* must be the last step, see the function comment */
pwq_dec_nr_in_flight(pwq, work_data);
}