From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Hocko Subject: Re: [PATCH -v2 2/5] OOM: thaw the OOM victim if it is frozen Date: Sun, 7 Dec 2014 11:45:39 +0100 Message-ID: <20141207104539.GK15892@dhcp22.suse.cz> References: <20141110163055.GC18373@dhcp22.suse.cz> <1417797707-31699-1-git-send-email-mhocko@suse.cz> <1417797707-31699-3-git-send-email-mhocko@suse.cz> <20141206130657.GC18711@htj.dyndns.org> <20141207102430.GF15892@dhcp22.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mail-wi0-f181.google.com ([209.85.212.181]:53578 "EHLO mail-wi0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753161AbaLGKpn (ORCPT ); Sun, 7 Dec 2014 05:45:43 -0500 Content-Disposition: inline In-Reply-To: <20141207102430.GF15892@dhcp22.suse.cz> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: Tejun Heo Cc: linux-mm@kvack.org, Andrew Morton , "\\\"Rafael J. Wysocki\\\"" , David Rientjes , Johannes Weiner , Oleg Nesterov , Cong Wang , LKML , linux-pm@vger.kernel.org On Sun 07-12-14 11:24:30, Michal Hocko wrote: > On Sat 06-12-14 08:06:57, Tejun Heo wrote: > > Hello, > > > > On Fri, Dec 05, 2014 at 05:41:44PM +0100, Michal Hocko wrote: > > > oom_kill_process only sets TIF_MEMDIE flag and sends a signal to the > > > victim. This is basically noop when the task is frozen though because > > > the task sleeps in uninterruptible sleep. The victim is eventually > > > thawed later when oom_scan_process_thread meets the task again in a > > > later OOM invocation so the OOM killer doesn't live lock. But this is > > > less than optimal. Let's add the frozen check and thaw the task right > > > before we send SIGKILL to the victim. > > > > > > The check and thawing in oom_scan_process_thread has to stay because the > > > task might got access to memory reserves even without an explicit > > > SIGKILL from oom_kill_process (e.g. it already has fatal signal pending > > > or it is exiting already). > > > > How else would a task get TIF_MEMDIE? If there are other paths which > > set TIF_MEMDIE, the right thing to do is creating a function which > > thaws / wakes up the target task and use it there too. Please > > interlock these things properly from the get-go instead of scattering > > these things around. > > See __out_of_memory which sets TIF_MEMDIE on current when it is exiting > or has fatal signals pending. This task cannot be frozen obviously. On the other hand we are doing the same early in oom_kill_process which doesn't work on the current. I've moved the __thaw_task into mark_tsk_oom_victim so it catches all instances now. oom_scan_process_thread doesn't need to thaw anymore. --- >>From af8222df6c503fa1beab8279ff39a282fd90698b Mon Sep 17 00:00:00 2001 From: Michal Hocko Date: Wed, 12 Nov 2014 18:56:54 +0100 Subject: [PATCH] OOM: thaw the OOM victim if it is frozen oom_kill_process only sets TIF_MEMDIE flag and sends a signal to the victim. This is basically noop when the task is frozen though because the task sleeps in uninterruptible sleep. The victim is eventually thawed later when oom_scan_process_thread meets the task again in a later OOM invocation so the OOM killer doesn't live lock. But this is less than optimal. Let's add __thaw_task into mark_tsk_oom_victim after we set TIF_MEMDIE to the victim. We are not checking whether the task is frozen because that would be racy and __thaw_task does that already. oom_scan_process_thread doesn't need to care about freezer anymore as TIF_MEMDIE and freezer are excluded completely now. Signed-off-by: Michal Hocko --- mm/oom_kill.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/mm/oom_kill.c b/mm/oom_kill.c index 56eab9621c3a..19a08f3f00ba 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -266,8 +266,6 @@ enum oom_scan_t oom_scan_process_thread(struct task_struct *task, * Don't allow any other task to have access to the reserves. */ if (test_tsk_thread_flag(task, TIF_MEMDIE)) { - if (unlikely(frozen(task))) - __thaw_task(task); if (!force_kill) return OOM_SCAN_ABORT; } @@ -428,6 +426,7 @@ void note_oom_kill(void) void mark_tsk_oom_victim(struct task_struct *tsk) { set_tsk_thread_flag(tsk, TIF_MEMDIE); + __thaw_task(tsk); } /** -- 2.1.3 -- Michal Hocko SUSE Labs