This is a note to let you know that I've just added the patch titled
mm: fix lost kswapd wakeup in kswapd_stop()
to the 3.0-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
mm-fix-lost-kswapd-wakeup-in-kswapd_stop.patch
and it can be found in the queue-3.0 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From 1c7e7f6c0703d03af6bcd5ccc11fc15d23e5ecbe Mon Sep 17 00:00:00 2001
From: Aaditya Kumar <[email protected]>
Date: Tue, 17 Jul 2012 15:48:07 -0700
Subject: mm: fix lost kswapd wakeup in kswapd_stop()
From: Aaditya Kumar <[email protected]>
commit 1c7e7f6c0703d03af6bcd5ccc11fc15d23e5ecbe upstream.
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 <[email protected]>
Acked-by: KOSAKI Motohiro <[email protected]>
Reviewed-by: Minchan Kim <[email protected]>
Acked-by: Mel Gorman <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
mm/vmscan.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2695,7 +2695,10 @@ 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)
Patches currently in stable-queue which might be from
[email protected] are
queue-3.0/mm-fix-lost-kswapd-wakeup-in-kswapd_stop.patch
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