From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f45.google.com (mail-wm0-f45.google.com [74.125.82.45]) by kanga.kvack.org (Postfix) with ESMTP id D05566B0005 for ; Fri, 19 Feb 2016 12:15:36 -0500 (EST) Received: by mail-wm0-f45.google.com with SMTP id g62so80486711wme.0 for ; Fri, 19 Feb 2016 09:15:36 -0800 (PST) Received: from mail-wm0-f50.google.com (mail-wm0-f50.google.com. [74.125.82.50]) by mx.google.com with ESMTPS id j142si14015942wmg.110.2016.02.19.09.15.35 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 19 Feb 2016 09:15:35 -0800 (PST) Received: by mail-wm0-f50.google.com with SMTP id g62so86510196wme.1 for ; Fri, 19 Feb 2016 09:15:35 -0800 (PST) Date: Fri, 19 Feb 2016 18:15:33 +0100 From: Michal Hocko Subject: Re: [PATCH] mm,oom: kill duplicated oom_unkillable_task() checks. Message-ID: <20160219171533.GA23376@dhcp22.suse.cz> References: <1455892411-7611-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> <20160219151043.GI12690@dhcp22.suse.cz> <201602200101.IBE90199.OSOFMFOLVtJQHF@I-love.SAKURA.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201602200101.IBE90199.OSOFMFOLVtJQHF@I-love.SAKURA.ne.jp> Sender: owner-linux-mm@kvack.org List-ID: To: Tetsuo Handa Cc: rientjes@google.com, hannes@cmpxchg.org, vdavydov@virtuozzo.com, linux-mm@kvack.org On Sat 20-02-16 01:01:36, Tetsuo Handa wrote: > Michal Hocko wrote: > > On Fri 19-02-16 23:33:31, Tetsuo Handa wrote: > > > Currently, oom_unkillable_task() is called for twice for each thread, > > > once at oom_scan_process_thread() and again at oom_badness(). > > > > > > The reason oom_scan_process_thread() needs to call oom_unkillable_task() > > > is to skip TIF_MEMDIE test and oom_task_origin() test if that thread is > > > not OOM-killable. > > > > > > But there is a problem with this ordering, for oom_task_origin() == true > > > will unconditionally select that thread regardless of oom_score_adj. > > > When we merge the OOM reaper, the OOM reaper will mark already reaped > > > process as OOM-unkillable by updating oom_score_adj. In order to avoid > > > falling into infinite loop, oom_score_adj needs to be checked before > > > doing oom_task_origin() test. > > > > What would be the infinite loop? > > Sequence until we merge the OOM reaper: > > (1) select_bad_process() returns p due to oom_task_origin(p) == true. > (2) oom_kill_process() sends SIGKILL to p and sets TIF_MEMDIE on p. > (3) p gets stuck at down_read(&mm->mmap_sem) in exit_mm(). > (4) The OOM killer will ignore TIF_MEMDIE on p after some timeout expires. > (5) select_bad_process() returns p again due to oom_task_origin(p) == true && > p->mm != NULL. And one more thing. The task will stop being oom_task_origin right after it detects signal pending and retuns from try_to_unuse resp. unmerge_and_remove_all_rmap_items. -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org