Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [ 03/41] mm: fix lost kswapd wakeup in kswapd_stop() | Date | Mon, 30 Jul 2012 10:31:02 -0700 |
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From: Greg KH <gregkh@linuxfoundation.org>
3.0-stable review patch. If anyone has any objections, please let me know.
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From: Aaditya Kumar <aaditya.kumar.30@gmail.com>
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>
--- 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)
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