Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932844AbcCVLBb (ORCPT ); Tue, 22 Mar 2016 07:01:31 -0400 Received: from mail-wm0-f68.google.com ([74.125.82.68]:36535 "EHLO mail-wm0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932767AbcCVLBM (ORCPT ); Tue, 22 Mar 2016 07:01:12 -0400 From: Michal Hocko To: Andrew Morton Cc: , LKML , Tetsuo Handa , David Rientjes , Michal Hocko Subject: [PATCH 8/9] oom: make oom_reaper freezable Date: Tue, 22 Mar 2016 12:00:25 +0100 Message-Id: <1458644426-22973-9-git-send-email-mhocko@kernel.org> X-Mailer: git-send-email 2.7.0 In-Reply-To: <1458644426-22973-1-git-send-email-mhocko@kernel.org> References: <1458644426-22973-1-git-send-email-mhocko@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1698 Lines: 56 From: Michal Hocko After "oom: clear TIF_MEMDIE after oom_reaper managed to unmap the address space" oom_reaper will call exit_oom_victim on the target task after it is done. This might however race with the PM freezer: CPU0 CPU1 CPU2 freeze_processes try_to_freeze_tasks # Allocation request out_of_memory oom_killer_disable wake_oom_reaper(P1) __oom_reap_task exit_oom_victim(P1) wait_event(oom_victims==0) [...] do_exit(P1) perform IO/interfere with the freezer which breaks the oom_killer_disable semantic. We no longer have a guarantee that the oom victim won't interfere with the freezer because it might be anywhere on the way to do_exit while the freezer thinks the task has already terminated. It might trigger IO or touch devices which are frozen already. In order to close this race, make the oom_reaper thread freezable. This will work because a) already running oom_reaper will block freezer to enter the quiescent state b) wake_oom_reaper will not wake up the reaper after it has been frozen c) the only way to call exit_oom_victim after try_to_freeze_tasks is from the oom victim's context when we know the further interference shouldn't be possible Signed-off-by: Michal Hocko --- mm/oom_kill.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/mm/oom_kill.c b/mm/oom_kill.c index af75260f32c3..bed2885d10b0 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -524,6 +524,8 @@ static void oom_reap_task(struct task_struct *tsk) static int oom_reaper(void *unused) { + set_freezable(); + while (true) { struct task_struct *tsk = NULL; -- 2.7.0