From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751866AbaLBJff (ORCPT ); Tue, 2 Dec 2014 04:35:35 -0500 Received: from mail-wi0-f180.google.com ([209.85.212.180]:58082 "EHLO mail-wi0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750998AbaLBJfd (ORCPT ); Tue, 2 Dec 2014 04:35:33 -0500 Date: Tue, 2 Dec 2014 10:35:30 +0100 From: Michal Hocko To: Oleg Nesterov Cc: Andrew Morton , Cong Wang , David Rientjes , "Rafael J. Wysocki" , Tejun Heo , linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] oom: kill the insufficient and no longer needed PT_TRACE_EXIT check Message-ID: <20141202093530.GC27014@dhcp22.suse.cz> References: <20141127230349.GA25075@redhat.com> <20141127230408.GA25100@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141127230408.GA25100@redhat.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 28-11-14 00:04:08, Oleg Nesterov wrote: > After the previous patch we can remove the PT_TRACE_EXIT check in > oom_scan_process_thread(), it was added to handle the case when the > coredumping was "frozen" by ptrace, but it doesn't really work. If > nothing else, we would need to check all threads which could share > the same ->mm to make it more or less correct. > > Signed-off-by: Oleg Nesterov I still do not see why we do not need task->ptrace & PT_TRACE_EXIT check here. I do understand that the check on group_leader doesn't make much sense. ptrace_event would block until the tracer let the task run again which may be never AFAICS. It is really sad how subtle and racy are all these checks :/ > --- > mm/oom_kill.c | 11 +++-------- > 1 files changed, 3 insertions(+), 8 deletions(-) > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > index 7af33b5..a2a4036 100644 > --- a/mm/oom_kill.c > +++ b/mm/oom_kill.c > @@ -287,14 +287,9 @@ enum oom_scan_t oom_scan_process_thread(struct task_struct *task, > if (oom_task_origin(task)) > return OOM_SCAN_SELECT; > > - if (task_will_free_mem(task) && !force_kill) { > - /* > - * If this task is not being ptraced on exit, then wait for it > - * to finish before killing some other task unnecessarily. > - */ > - if (!(task->group_leader->ptrace & PT_TRACE_EXIT)) > - return OOM_SCAN_ABORT; > - } > + if (task_will_free_mem(task) && !force_kill) > + return OOM_SCAN_ABORT; > + > return OOM_SCAN_OK; > } > > -- > 1.5.5.1 > -- Michal Hocko SUSE Labs