Commit 34a06bd6 authored by Tejun Heo's avatar Tejun Heo
Browse files

workqueue: replace POOL_MANAGING_WORKERS flag with worker_pool->manager_arb 



POOL_MANAGING_WORKERS is used to synchronize the manager role.
Synchronizing among workers doesn't need blocking and that's why it's
implemented as a flag.

It got converted to a mutex a while back to add blocking wait from CPU
hotplug path - 60373152 ("workqueue: use mutex for global_cwq
manager exclusion").  Later it turned out that synchronization among
workers and cpu hotplug need to be done separately.  Eventually,
POOL_MANAGING_WORKERS is restored and workqueue->manager_mutex got
morphed into workqueue->assoc_mutex - 552a37e9 ("workqueue: restore
POOL_MANAGING_WORKERS") and b2eb83d1 ("workqueue: rename
manager_mutex to assoc_mutex").

Now, we're gonna need to be able to lock out managers from
destroy_workqueue() to support multiple unbound pools with custom
attributes making it again necessary to be able to block on the
manager role.  This patch replaces POOL_MANAGING_WORKERS with
worker_pool->manager_arb.

This patch doesn't introduce any behavior changes.

v2: s/manager_mutex/manager_arb/

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent fa1b54e6

kernel/workqueue.c

+10 −11
Original line number Diff line number Diff line
@@ -64,7 +64,6 @@ enum { 
	 * create_worker() is in progress.

	 */

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

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

	POOL_DISASSOCIATED	= 1 << 2,	/* cpu can't serve workers */

	POOL_FREEZING		= 1 << 3,	/* freeze in progress */
@@ -145,6 +144,7 @@ struct worker_pool { 
	DECLARE_HASHTABLE(busy_hash, BUSY_WORKER_HASH_ORDER);

						/* L: hash of busy workers */



	struct mutex		manager_arb;	/* manager arbitration */

	struct mutex		assoc_mutex;	/* protect POOL_DISASSOCIATED */

	struct ida		worker_ida;	/* L: for worker IDs */
@@ -706,7 +706,7 @@ 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 = pool->flags & POOL_MANAGING_WORKERS;

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

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

	int nr_busy = pool->nr_workers - nr_idle;
@@ -2029,19 +2029,17 @@ static bool manage_workers(struct worker *worker) 
	struct worker_pool *pool = worker->pool;

	bool ret = false;



	if (pool->flags & POOL_MANAGING_WORKERS)

	if (!mutex_trylock(&pool->manager_arb))

		return ret;



	pool->flags |= POOL_MANAGING_WORKERS;



	/*

	 * To simplify both worker management and CPU hotplug, hold off

	 * management while hotplug is in progress.  CPU hotplug path can't

	 * grab %POOL_MANAGING_WORKERS to achieve this because that can

	 * lead to idle worker depletion (all become busy thinking someone

	 * else is managing) which in turn can result in deadlock under

	 * extreme circumstances.  Use @pool->assoc_mutex to synchronize

	 * manager against CPU hotplug.

	 * grab @pool->manager_arb to achieve this because that can lead to

	 * idle worker depletion (all become busy thinking someone else is

	 * managing) which in turn can result in deadlock under extreme

	 * circumstances.  Use @pool->assoc_mutex to synchronize manager

	 * against CPU hotplug.

	 *

	 * assoc_mutex would always be free unless CPU hotplug is in

	 * progress.  trylock first without dropping @pool->lock.
@@ -2077,8 +2075,8 @@ 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->assoc_mutex);

	mutex_unlock(&pool->manager_arb);

	return ret;

}
@@ -3806,6 +3804,7 @@ static int __init init_workqueues(void) 
			setup_timer(&pool->mayday_timer, pool_mayday_timeout,

				    (unsigned long)pool);



			mutex_init(&pool->manager_arb);

			mutex_init(&pool->assoc_mutex);

			ida_init(&pool->worker_ida);

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