* Re: [PATCH] mm: offlining memory may block forever
2012-06-20 16:23 [PATCH] mm: offlining memory may block forever Aaditya Kumar
@ 2012-06-20 17:13 ` Greg KH
2012-06-20 18:49 ` KOSAKI Motohiro
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: Greg KH @ 2012-06-20 17:13 UTC (permalink / raw)
To: Aaditya Kumar
Cc: KOSAKI Motohiro, linux-kernel, linux-mm, stable, kosaki.motohiro,
Mel Gorman, KAMEZAWA Hiroyuki, Minchan Kim, Michal Hocko,
tim.bird, frank.rowand, takuzo.ohara, kan.iibuchi, aaditya.kumar
On Wed, Jun 20, 2012 at 09:53:31PM +0530, Aaditya Kumar wrote:
> Offlining memory may block forever, waiting for kswapd() to wake up because
> kswapd() does not check the event kthread->should_stop before sleeping.
>
> The proper pattern, from Documentation/memory-barriers.txt, is:
> --- waker ---
> event_indicated = 1;
> wake_up_process(event_daemon);
>
> --- sleeper ---
> for (;;) {
> set_current_state(TASK_UNINTERRUPTIBLE);
> if (event_indicated)
> break;
> schedule();
> }
>
> set_current_state() may be wrapped by:
> prepare_to_wait();
>
> In the kswapd() case, event_indicated is kthread->should_stop.
> --- offlining memory (waker) ---
> kswapd_stop()
> kthread_stop()
> kthread->should_stop = 1
> wake_up_process()
> wait_for_completion()
>
>
> --- kswapd_try_to_sleep (sleeper) ---
> kswapd_try_to_sleep()
> prepare_to_wait()
> .
> .
> schedule()
> .
> .
> finish_wait()
>
> The schedule() needs to be protected by a test of kthread->should_stop,
> which is wrapped by kthread_should_stop().
>
> Reproducer:
> Do heavy file I/O in background.
> Do a memory offline/online in a tight loop
>
>
> Signed-off-by: Aaditya Kumar <aaditya.kumar@ap.sony.com>
<formletter>
This is not the correct way to submit patches for inclusion in the
stable kernel tree. Please read Documentation/stable_kernel_rules.txt
for how to do this properly.
</formletter>
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH] mm: offlining memory may block forever
2012-06-20 16:23 [PATCH] mm: offlining memory may block forever Aaditya Kumar
2012-06-20 17:13 ` Greg KH
@ 2012-06-20 18:49 ` KOSAKI Motohiro
2012-06-21 1:37 ` Minchan Kim
2012-06-21 13:04 ` Mel Gorman
3 siblings, 0 replies; 5+ messages in thread
From: KOSAKI Motohiro @ 2012-06-20 18:49 UTC (permalink / raw)
To: aaditya.kumar.30
Cc: kosaki.motohiro, linux-kernel, linux-mm, stable, kosaki.motohiro,
gregkh, mel, kamezawa.hiroyu, minchan, mhocko, tim.bird,
frank.rowand, takuzo.ohara, kan.iibuchi, aaditya.kumar
On 6/20/2012 12:23 PM, Aaditya Kumar wrote:
> Offlining memory may block forever, waiting for kswapd() to wake up because
> kswapd() does not check the event kthread->should_stop before sleeping.
>
> The proper pattern, from Documentation/memory-barriers.txt, is:
> --- waker ---
> event_indicated = 1;
> wake_up_process(event_daemon);
>
> --- sleeper ---
> for (;;) {
> set_current_state(TASK_UNINTERRUPTIBLE);
> if (event_indicated)
> break;
> schedule();
> }
>
> set_current_state() may be wrapped by:
> prepare_to_wait();
>
> In the kswapd() case, event_indicated is kthread->should_stop.
> --- offlining memory (waker) ---
Please avoid "---". This is used for a separator between a patch
description and code.
Other than that,
Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> kswapd_stop()
> kthread_stop()
> kthread->should_stop = 1
> wake_up_process()
> wait_for_completion()
>
>
> --- kswapd_try_to_sleep (sleeper) ---
> kswapd_try_to_sleep()
> prepare_to_wait()
> .
> .
> schedule()
> .
> .
> finish_wait()
>
> The schedule() needs to be protected by a test of kthread->should_stop,
> which is wrapped by kthread_should_stop().
>
> Reproducer:
> Do heavy file I/O in background.
> Do a memory offline/online in a tight loop
>
>
> Signed-off-by: Aaditya Kumar <aaditya.kumar@ap.sony.com>
>
> ---
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index eeb3bc9..b60691e 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2688,7 +2688,10 @@ static void kswapd_try_to_sleep(pg_data_t
> *pgdat, int order, int classzone_idx)
> * them before going back to sleep.
> */
> set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold);
> - schedule();
> +
> + if (!kthread_should_stop())
> + schedule();
> +
> set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold);
> } else {
> if (remaining)
>
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH] mm: offlining memory may block forever
2012-06-20 16:23 [PATCH] mm: offlining memory may block forever Aaditya Kumar
2012-06-20 17:13 ` Greg KH
2012-06-20 18:49 ` KOSAKI Motohiro
@ 2012-06-21 1:37 ` Minchan Kim
2012-06-21 13:04 ` Mel Gorman
3 siblings, 0 replies; 5+ messages in thread
From: Minchan Kim @ 2012-06-21 1:37 UTC (permalink / raw)
To: Aaditya Kumar
Cc: KOSAKI Motohiro, linux-kernel, linux-mm, stable, kosaki.motohiro,
gregkh, Mel Gorman, KAMEZAWA Hiroyuki, Michal Hocko, tim.bird,
frank.rowand, takuzo.ohara, kan.iibuchi, aaditya.kumar
On 06/21/2012 01:23 AM, Aaditya Kumar wrote:
> Offlining memory may block forever, waiting for kswapd() to wake up because
> kswapd() does not check the event kthread->should_stop before sleeping.
>
> The proper pattern, from Documentation/memory-barriers.txt, is:
> --- waker ---
> event_indicated = 1;
> wake_up_process(event_daemon);
>
> --- sleeper ---
> for (;;) {
> set_current_state(TASK_UNINTERRUPTIBLE);
> if (event_indicated)
> break;
> schedule();
> }
>
> set_current_state() may be wrapped by:
> prepare_to_wait();
>
> In the kswapd() case, event_indicated is kthread->should_stop.
> --- offlining memory (waker) ---
> kswapd_stop()
> kthread_stop()
> kthread->should_stop = 1
> wake_up_process()
> wait_for_completion()
>
>
> --- kswapd_try_to_sleep (sleeper) ---
> kswapd_try_to_sleep()
> prepare_to_wait()
> .
> .
> schedule()
> .
> .
> finish_wait()
>
> The schedule() needs to be protected by a test of kthread->should_stop,
> which is wrapped by kthread_should_stop().
>
> Reproducer:
> Do heavy file I/O in background.
> Do a memory offline/online in a tight loop
>
>
> Signed-off-by: Aaditya Kumar <aaditya.kumar@ap.sony.com>
Reviewed-by: Minchan Kim <minchan@kernel.org>
Nitpick: We can remove kthread_should_stop check earlier in kswapd_try_to_sleep.
But it's no biggie. And I hope you change patch title
Title : Fix loss of kswapd wakeup in kswapd_stop
Description: Offlining memory may block forever because blah, blah, blah.
--
Kind regards,
Minchan Kim
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH] mm: offlining memory may block forever
2012-06-20 16:23 [PATCH] mm: offlining memory may block forever Aaditya Kumar
` (2 preceding siblings ...)
2012-06-21 1:37 ` Minchan Kim
@ 2012-06-21 13:04 ` Mel Gorman
3 siblings, 0 replies; 5+ messages in thread
From: Mel Gorman @ 2012-06-21 13:04 UTC (permalink / raw)
To: Aaditya Kumar
Cc: KOSAKI Motohiro, linux-kernel, linux-mm, stable, kosaki.motohiro,
gregkh, KAMEZAWA Hiroyuki, Minchan Kim, Michal Hocko, tim.bird,
frank.rowand, takuzo.ohara, kan.iibuchi, aaditya.kumar
On Wed, Jun 20, 2012 at 09:53:31PM +0530, Aaditya Kumar wrote:
> Offlining memory may block forever, waiting for kswapd() to wake up because
> kswapd() does not check the event kthread->should_stop before sleeping.
>
Acked-by: Mel Gorman <mel@csn.ul.ie>
--
Mel Gorman
SUSE Labs
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
^ permalink raw reply [flat|nested] 5+ messages in thread