From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752729AbbJEQht (ORCPT ); Mon, 5 Oct 2015 12:37:49 -0400 Received: from mx1.redhat.com ([209.132.183.28]:54863 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752579AbbJEQhn (ORCPT ); Mon, 5 Oct 2015 12:37:43 -0400 Date: Mon, 5 Oct 2015 18:34:27 +0200 From: Oleg Nesterov To: Andrew Morton Cc: David Rientjes , Kyle Walker , Michal Hocko , Stanislav Kozina , Tetsuo Handa , linux-kernel@vger.kernel.org Subject: [PATCH -mm] mm/oom_kill: change oom_kill_process() to bump ->mm_count rather than ->mm_users Message-ID: <20151005163427.GA20595@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org oom_kill_process() does atomic_inc(&mm->mm_users) to ensure that this ->mm can't go away and this is wrong, change it to rely on ->mm_count and mmdrop(). Firstly, we do not want to delay exit_mmap/etc if the victim exits before we do mmput(), but this is minor. More importantly, we simply can not do mmput() in oom_kill_process(), this can deadlock. For example, suppose that access_process_vm(tsk) triggers OOM and oom-killer decides to kill this "tsk". If it exits and does mmput() before us, ksm_exit() called by us may want to want to take the same mmap_sem for writing. Signed-off-by: Oleg Nesterov --- mm/oom_kill.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/mm/oom_kill.c b/mm/oom_kill.c index 034d219..52abb78 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -571,7 +571,7 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p, /* Get a reference to safely compare mm after task_unlock(victim) */ mm = victim->mm; - atomic_inc(&mm->mm_users); + atomic_inc(&mm->mm_count); /* * We should send SIGKILL before setting TIF_MEMDIE in order to prevent * the OOM victim from depleting the memory reserves from the user @@ -609,7 +609,7 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p, } rcu_read_unlock(); - mmput(mm); + mmdrop(mm); put_task_struct(victim); } #undef K -- 2.4.3