The patch titled
Subject: mm: fix lost kswapd wakeup in kswapd_stop()
has been added to the -mm tree. Its filename is
mm-fix-lost-kswapd-wakeup-in-kswapd_stop.patch
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------------------------------------------------------
From: Aaditya Kumar <aaditya.kumar.30@xxxxxxxxx>
Subject: mm: fix lost kswapd wakeup in kswapd_stop()
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@xxxxxxxxxxx>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Reviewed-by: Minchan Kim <minchan@xxxxxxxxxx>
Acked-by: Mel Gorman <mel@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmscan.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff -puN mm/vmscan.c~mm-fix-lost-kswapd-wakeup-in-kswapd_stop mm/vmscan.c
--- a/mm/vmscan.c~mm-fix-lost-kswapd-wakeup-in-kswapd_stop
+++ a/mm/vmscan.c
@@ -2706,7 +2706,10 @@ static void kswapd_try_to_sleep(pg_data_
* 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)
_
Subject: Subject: mm: fix lost kswapd wakeup in kswapd_stop()
Patches currently in -mm which might be from aaditya.kumar.30@xxxxxxxxx are
mm-fix-lost-kswapd-wakeup-in-kswapd_stop.patch
memory-hotplug-fix-kswapd-looping-forever-problem.patch
memory-hotplug-fix-kswapd-looping-forever-problem-fix.patch
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