[PATCH] workqueue: remove the del_timer_sync()s in maybe_create_worker()

From: Lai Jiangshan
Date: Sun Jul 13 2014 - 11:30:30 EST

It is said in the document that the timer which is being
deleted by del_timer_sync() should not be restarted:
Synchronization rules: Callers must prevent restarting of
the timer, otherwise this function is meaningless.

Repeating timer may cause the del_timer_sync() spin longer,
or even spin forever in very very very very extreme condition.

It is not considered a bug for me, but it disobeys the document.

To fix it, we need:
1) don't requeue the mayday timer when !need_to_create_worker()
it is a preparation/cleaup step for the fix. Otherwise the timer
will repeat forever if we only do the 2).
2) remove the del_timer_sync()s in maybe_create_worker()
Fix the problem. It is not enough if we only do the 1),
need_to_create_worker() would be probably true when the time
del_timer_sync() is called, the timer is still repeating.

Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
kernel/workqueue.c | 6 ++----
1 files changed, 2 insertions(+), 4 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 35974ac..593b9bc 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1866,12 +1866,12 @@ static void pool_mayday_timeout(unsigned long __pool)
list_for_each_entry(work, &pool->worklist, entry)
+ mod_timer(&pool->mayday_timer, jiffies + MAYDAY_INTERVAL);

- mod_timer(&pool->mayday_timer, jiffies + MAYDAY_INTERVAL);

@@ -1913,7 +1913,6 @@ restart:

worker = create_worker(pool);
if (worker) {
- del_timer_sync(&pool->mayday_timer);
if (WARN_ON_ONCE(need_to_create_worker(pool)))
@@ -1931,7 +1930,6 @@ restart:

- del_timer_sync(&pool->mayday_timer);
if (need_to_create_worker(pool))
goto restart;

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