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@tv-sign.ru>
Cc: Dmitry Adamushko <dmitry.adamushko@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index ec7e4f62aaff4e71051eefb7d684e8ff4868a5ad..4a26a1382df05febed4a94bce11be2bc2a46b648 100644 (file)
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -830,10 +830,21 @@ struct workqueue_struct *__create_workqueue_key(const char *name,
                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))