Messages in this thread Patch in this message | | | Date | Wed, 20 Jun 2012 21:53:31 +0530 | Subject | [PATCH] mm: offlining memory may block forever | From | Aaditya Kumar <> |
| |
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>
--- 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)
| |