Re: [PATCH] sched: don't clear PF_THREAD_BOUND in select_fallback_rq

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

* Sebastian Andrzej Siewior | 2013-06-07 22:50:48 [+0200]:

>* Qiang Huang | 2013-04-25 17:01:18 [+0800]:
>
>>select_fallback_rq() is called and PF_THREAD_BOUND is cleared. In my
>>box, 1/3 bounded kernel threads will clear that flag after boot.
>
>Please tell me _which_ threads lose this flag. I don't see this…

The only way I lose this flag is by starting a workqueue on a CPU which
if offline. Now that is wrong. I am not sure if the workqueue re-uses
the "idle" workers later. In the up path it sets the CPU mask and
PF_THREAD_BOUND is usually set (unless it was lost due to
select_fallback_rq()). So we can set this back on:

Subject: [PATCH] kernel/workqueue: Add PF_THREAD_BOUND after set_cpu

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 kernel/workqueue.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 11285e4..aff5841 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1637,8 +1637,10 @@ __acquires(&gcwq->lock)
 		 * it races with cpu hotunplug operation.  Verify
 		 * against GCWQ_DISASSOCIATED.
 		 */
-		if (!(gcwq->flags & GCWQ_DISASSOCIATED))
+		if (!(gcwq->flags & GCWQ_DISASSOCIATED)) {
 			set_cpus_allowed_ptr(task, get_cpu_mask(gcwq->cpu));
+			task->flags |= PF_THREAD_BOUND;
+		}
 
 		spin_lock_irq(&gcwq->lock);
 		if (gcwq->flags & GCWQ_DISASSOCIATED)
-- 
1.7.10.4

Do you see any other?

Sebastian
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