From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754678Ab2G3RcV (ORCPT ); Mon, 30 Jul 2012 13:32:21 -0400 Received: from mail-pb0-f46.google.com ([209.85.160.46]:38517 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754534Ab2G3RcR (ORCPT ); Mon, 30 Jul 2012 13:32:17 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Greg KH , torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Aaditya Kumar , KOSAKI Motohiro , Minchan Kim , Mel Gorman Subject: [ 03/41] mm: fix lost kswapd wakeup in kswapd_stop() Date: Mon, 30 Jul 2012 10:31:02 -0700 Message-Id: <20120730172901.577904115@linuxfoundation.org> X-Mailer: git-send-email 1.7.10.1.362.g242cab3 In-Reply-To: <20120730172901.306897424@linuxfoundation.org> References: <20120730172901.306897424@linuxfoundation.org> User-Agent: quilt/0.60-20.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Greg KH 3.0-stable review patch. If anyone has any objections, please let me know. ------------------ From: Aaditya Kumar 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 Acked-by: KOSAKI Motohiro Reviewed-by: Minchan Kim Acked-by: Mel Gorman Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- 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)