From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with ESMTP id A41C88D003A for ; Mon, 14 Mar 2011 16:22:30 -0400 (EDT) Received: from hpaq7.eem.corp.google.com (hpaq7.eem.corp.google.com [172.25.149.7]) by smtp-out.google.com with ESMTP id p2EKMQ2g013429 for ; Mon, 14 Mar 2011 13:22:26 -0700 Received: from pvg12 (pvg12.prod.google.com [10.241.210.140]) by hpaq7.eem.corp.google.com with ESMTP id p2EKM6la003578 (version=TLSv1/SSLv3 cipher=RC4-SHA bits=128 verify=NOT) for ; Mon, 14 Mar 2011 13:22:24 -0700 Received: by pvg12 with SMTP id 12so1078573pvg.33 for ; Mon, 14 Mar 2011 13:22:20 -0700 (PDT) Date: Mon, 14 Mar 2011 13:22:17 -0700 (PDT) From: David Rientjes Subject: Re: [PATCH 1/3 for 2.6.38] oom: oom_kill_process: don't set TIF_MEMDIE if !p->mm In-Reply-To: <20110314190446.GB21845@redhat.com> Message-ID: References: <20110303100030.B936.A69D9226@jp.fujitsu.com> <20110308134233.GA26884@redhat.com> <20110309151946.dea51cde.akpm@linux-foundation.org> <20110312123413.GA18351@redhat.com> <20110312134341.GA27275@redhat.com> <20110313212726.GA24530@redhat.com> <20110314190419.GA21845@redhat.com> <20110314190446.GB21845@redhat.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Oleg Nesterov Cc: Hugh Dickins , Linus Torvalds , Andrew Morton , KOSAKI Motohiro , KAMEZAWA Hiroyuki , Andrey Vagin , Frantisek Hrbata , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Mon, 14 Mar 2011, Oleg Nesterov wrote: > oom_kill_process() simply sets TIF_MEMDIE and returns if PF_EXITING. > This is very wrong by many reasons. In particular, this thread can > be the dead group leader. Check p->mm != NULL. > This is true only for the oom_kill_allocating_task sysctl where it is required in all cases to kill current; current won't be triggering the oom killer if it's dead. oom_kill_process() is called with the thread selected by select_bad_process() and that function will not return any thread if any eligible task is found to be PF_EXITING and is not current, or any eligible task is found to have TIF_MEMDIE. In other words, for this conditional to be true in oom_kill_process(), then p must be current and so it cannot be the dead group leader as specified in your changelog unless PF_EXITING gets set between select_bad_process() and the oom_kill_process() call: we don't care about that since it's in the exit path and we therefore want to give it access to memory reserves to quickly exit anyway and the check for PF_EXITING in select_bad_process() prevents any infinite loop of that task getting constantly reselected if it's dead. > Note: this is _not_ enough. Just a minimal fix. > > Signed-off-by: Oleg Nesterov > --- > > mm/oom_kill.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > --- 38/mm/oom_kill.c~1_kill_fix_pf_exiting 2011-03-14 17:53:05.000000000 +0100 > +++ 38/mm/oom_kill.c 2011-03-14 18:51:49.000000000 +0100 > @@ -470,7 +470,7 @@ static int oom_kill_process(struct task_ > * If the task is already exiting, don't alarm the sysadmin or kill > * its children or threads, just set TIF_MEMDIE so it can die quickly > */ > - if (p->flags & PF_EXITING) { > + if (p->flags & PF_EXITING && p->mm) { > set_tsk_thread_flag(p, TIF_MEMDIE); > boost_dying_task_prio(p, mem); > return 0; > > -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org