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Commit 552a37e9 authored by Lai Jiangshan's avatar Lai Jiangshan Committed by Tejun Heo
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workqueue: restore POOL_MANAGING_WORKERS 



This patch restores POOL_MANAGING_WORKERS which was replaced by
pool->manager_mutex by 60373152 "workqueue: use mutex for global_cwq
manager exclusion".

There's a subtle idle worker depletion bug across CPU hotplug events
and we need to distinguish an actual manager and CPU hotplug
preventing management.  POOL_MANAGING_WORKERS will be used for the
former and manager_mutex the later.

This patch just lays POOL_MANAGING_WORKERS on top of the existing
manager_mutex and doesn't introduce any synchronization changes.  The
next patch will update it.

Note that this patch fixes a non-critical anomaly where
too_many_workers() may return %true spuriously while CPU hotplug is in
progress.  While the issue could schedule idle timer spuriously, it
didn't trigger any actual misbehavior.

tj: Rewrote patch description.

Signed-off-by: default avatarLai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent ec58815a

kernel/workqueue.c

+4 −1
Original line number Diff line number Diff line
@@ -66,6 +66,7 @@ enum { 


	/* pool flags */

	POOL_MANAGE_WORKERS	= 1 << 0,	/* need to manage workers */

	POOL_MANAGING_WORKERS   = 1 << 1,       /* managing workers */



	/* worker flags */

	WORKER_STARTED		= 1 << 0,	/* started */
@@ -652,7 +653,7 @@ static bool need_to_manage_workers(struct worker_pool *pool) 
/* Do we have too many workers and should some go away? */

static bool too_many_workers(struct worker_pool *pool)

{

	bool managing = mutex_is_locked(&pool->manager_mutex);

	bool managing = pool->flags & POOL_MANAGING_WORKERS;

	int nr_idle = pool->nr_idle + managing; /* manager is considered idle */

	int nr_busy = pool->nr_workers - nr_idle;
@@ -1827,6 +1828,7 @@ static bool manage_workers(struct worker *worker) 
	if (!mutex_trylock(&pool->manager_mutex))

		return ret;



	pool->flags |= POOL_MANAGING_WORKERS;

	pool->flags &= ~POOL_MANAGE_WORKERS;



	/*
@@ -1836,6 +1838,7 @@ static bool manage_workers(struct worker *worker) 
	ret |= maybe_destroy_workers(pool);

	ret |= maybe_create_worker(pool);



	pool->flags &= ~POOL_MANAGING_WORKERS;

	mutex_unlock(&pool->manager_mutex);

	return ret;

}