linux-kernel - [PATCH 14/31] workqueue: replace POOL_MANAGING_WORKERS flag with worker_pool->manager

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Date:	Fri,  1 Mar 2013 19:24:05 -0800
From:	Tejun Heo <tj@...nel.org>
To:	linux-kernel@...r.kernel.org, laijs@...fujitsu.com
Cc:	axboe@...nel.dk, jmoyer@...hat.com, zab@...hat.com,
	Tejun Heo <tj@...nel.org>
Subject: [PATCH 14/31] workqueue: replace POOL_MANAGING_WORKERS flag with worker_pool->manager_mutex

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 - 6037315269 ("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 - 552a37e936 ("workqueue: restore
POOL_MANAGING_WORKERS") and b2eb83d123 ("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_mutex.

This patch doesn't introduce any behavior changes.

Signed-off-by: Tejun Heo <tj@...nel.org>
---
 kernel/workqueue.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 2645218..68b3443 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -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_mutex;	/* the holder is the manager */
 	struct mutex		assoc_mutex;	/* protect POOL_DISASSOCIATED */
 	struct ida		worker_ida;	/* L: for worker IDs */
 
@@ -702,7 +702,7 @@ 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_mutex);
 	int nr_idle = pool->nr_idle + managing; /* manager is considered idle */
 	int nr_busy = pool->nr_workers - nr_idle;
 
@@ -2027,15 +2027,13 @@ 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_mutex))
 		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
+	 * grab @pool->manager_mutex 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
@@ -2075,8 +2073,8 @@ 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_mutex);
 	return ret;
 }
 
@@ -3805,6 +3803,7 @@ static int __init init_workqueues(void)
 			setup_timer(&pool->mayday_timer, pool_mayday_timeout,
 				    (unsigned long)pool);
 
+			mutex_init(&pool->manager_mutex);
 			mutex_init(&pool->assoc_mutex);
 			ida_init(&pool->worker_ida);
 
-- 
1.8.1.2

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