From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk0-f199.google.com (mail-qk0-f199.google.com [209.85.220.199]) by kanga.kvack.org (Postfix) with ESMTP id B3FFE6B0253 for ; Mon, 27 Jun 2016 11:50:43 -0400 (EDT) Received: by mail-qk0-f199.google.com with SMTP id d2so217302693qkg.0 for ; Mon, 27 Jun 2016 08:50:43 -0700 (PDT) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id k83si13547838qkh.95.2016.06.27.08.50.42 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 27 Jun 2016 08:50:42 -0700 (PDT) Date: Mon, 27 Jun 2016 17:51:20 +0200 From: Oleg Nesterov Subject: Re: [PATCH] mm,oom: use per signal_struct flag rather than clear TIF_MEMDIE Message-ID: <20160627155119.GA17686@redhat.com> References: <1466766121-8164-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> <20160624215627.GA1148@redhat.com> <201606251444.EGJ69787.FtMOFJOLSHFQOV@I-love.SAKURA.ne.jp> <20160627092326.GD31799@dhcp22.suse.cz> <20160627103609.GE31799@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160627103609.GE31799@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Tetsuo Handa , linux-mm@kvack.org, vdavydov@virtuozzo.com, rientjes@google.com On 06/27, Michal Hocko wrote: > > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -237,6 +237,8 @@ void free_task(struct task_struct *tsk) > ftrace_graph_exit_task(tsk); > put_seccomp_filter(tsk); > arch_release_task_struct(tsk); > + if (tsk->active_mm) > + mmdrop(tsk->active_mm); > free_task_struct(tsk); > } > EXPORT_SYMBOL(free_task); > @@ -1022,6 +1024,8 @@ static int copy_mm(unsigned long clone_flags, struct task_struct *tsk) > good_mm: > tsk->mm = mm; > tsk->active_mm = mm; > + /* to be release in the final task_put */ > + atomic_inc(&mm->mm_count); > return 0; No, I don't think this can work. Note that tsk->active_mm in free_task() points to the random mm "borrowed" from the previous/random task in context_switch() if task->mm == NULL. This is true for kthreads and for the task which has already called exit_mm(). > - p = find_lock_task_mm(tsk); > - if (!p) > - goto unlock_oom; > - mm = p->mm; > + task_lock(tsk); > + mm = tsk->active_mm; The same. We can't know where this ->active_mm points to. Just suppose that this tsk schedules after exit_mm(). When it gets CPU again tsk->active_mm will point to ->mm of another task which in turns called schedule() to make this tsk active. Yes I agree, it would be nice to remove find_lock_task_mm(). And in fact it would be nice to kill task_struct->mm (but this needs a lot of cleanups). We probably want signal_struct->mm, but this is a bit complicated (locking). Oleg. -- 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