lkml.org 
[lkml]   [2012]   [May]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[ 059/117] workqueue: skip nr_running sanity check in worker_enter_idle() if trustee is active
3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Tejun Heo <tj@kernel.org>

commit 544ecf310f0e7f51fa057ac2a295fc1b3b35a9d3 upstream.

worker_enter_idle() has WARN_ON_ONCE() which triggers if nr_running
isn't zero when every worker is idle. This can trigger spuriously
while a cpu is going down due to the way trustee sets %WORKER_ROGUE
and zaps nr_running.

It first sets %WORKER_ROGUE on all workers without updating
nr_running, releases gcwq->lock, schedules, regrabs gcwq->lock and
then zaps nr_running. If the last running worker enters idle
inbetween, it would see stale nr_running which hasn't been zapped yet
and trigger the WARN_ON_ONCE().

Fix it by performing the sanity check iff the trustee is idle.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
kernel/workqueue.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 211eadb..c36c86c 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1213,8 +1213,13 @@ static void worker_enter_idle(struct worker *worker)
} else
wake_up_all(&gcwq->trustee_wait);

- /* sanity check nr_running */
- WARN_ON_ONCE(gcwq->nr_workers == gcwq->nr_idle &&
+ /*
+ * Sanity check nr_running. Because trustee releases gcwq->lock
+ * between setting %WORKER_ROGUE and zapping nr_running, the
+ * warning may trigger spuriously. Check iff trustee is idle.
+ */
+ WARN_ON_ONCE(gcwq->trustee_state == TRUSTEE_DONE &&
+ gcwq->nr_workers == gcwq->nr_idle &&
atomic_read(get_gcwq_nr_running(gcwq->cpu)));
}




\
 
 \ /
  Last update: 2012-05-28 06:01    [W:0.824 / U:0.536 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site