linux-kernel - [PATCH] workqueues: add comments to __create_workqueue

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Message-ID: <20080729162246.GB412@tv-sign.ru>
Date:	Tue, 29 Jul 2008 20:22:46 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>
Subject: [PATCH] workqueues: add comments to __create_workqueue_key()

Dmitry Adamushko pointed out that the error handling in
__create_workqueue_key() is not clear, add the comment.

Signed-off-by: Oleg Nesterov <oleg@...sign.ru>

--- LINUS/kernel/workqueue.c~	2008-07-29 17:59:48.000000000 +0400
+++ LINUS/kernel/workqueue.c	2008-07-29 18:41:06.000000000 +0400
@@ -830,10 +830,21 @@ struct workqueue_struct *__create_workqu
 		start_workqueue_thread(cwq, -1);
 	} else {
 		cpu_maps_update_begin();
+		/*
+		 * We must place this wq on list even if the code below fails.
+		 * cpu_down(cpu) can remove cpu from cpu_populated_map before
+		 * destroy_workqueue() takes the lock, in that case we leak
+		 * cwq[cpu]->thread.
+		 */
 		spin_lock(&workqueue_lock);
 		list_add(&wq->list, &workqueues);
 		spin_unlock(&workqueue_lock);
-
+		/*
+		 * We must initialize cwqs for each possible cpu even if we
+		 * are going to call destroy_workqueue() finally. Otherwise
+		 * cpu_up() can hit the uninitialized cwq once we drop the
+		 * lock.
+		 */
 		for_each_possible_cpu(cpu) {
 			cwq = init_cpu_workqueue(wq, cpu);
 			if (err || !cpu_online(cpu))

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