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authorAaditya Kumar <aaditya.kumar.30@gmail.com>2012-07-17 15:48:07 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2012-08-01 12:26:54 -0700
commit6d40de834ce9bb2964a70b7f91a98406eceb0399 (patch)
treed82f496a2c3d125136c4c7d2eef5bceec7943964 /mm/vmscan.c
parentdccecc646f06f06db8c32fc6615fee847852cec6 (diff)
mm: fix lost kswapd wakeup in kswapd_stop()
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 <aaditya.kumar@ap.sony.com> Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Reviewed-by: Minchan Kim <minchan@kernel.org> Acked-by: Mel Gorman <mel@csn.ul.ie> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'mm/vmscan.c')
-rw-r--r--mm/vmscan.c5
1 files changed, 4 insertions, 1 deletions
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 1b0ed361e5bf..130fa32441c0 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2695,7 +2695,10 @@ 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)