From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933197AbbJAM4x (ORCPT ); Thu, 1 Oct 2015 08:56:53 -0400 Received: from mail-wi0-f171.google.com ([209.85.212.171]:35533 "EHLO mail-wi0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756209AbbJAM4u (ORCPT ); Thu, 1 Oct 2015 08:56:50 -0400 Date: Thu, 1 Oct 2015 14:56:48 +0200 From: Michal Hocko To: Oleg Nesterov Cc: Andrew Morton , David Rientjes , Kyle Walker , Stanislav Kozina , Tetsuo Handa , linux-kernel@vger.kernel.org Subject: Re: [PATCH -mm v2 3/3] mm/oom_kill: fix the wrong task->mm == mm checks in oom_kill_process() Message-ID: <20151001125647.GE24077@dhcp22.suse.cz> References: <20150930182341.GA15047@redhat.com> <20150930182411.GA15250@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150930182411.GA15250@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 Wed 30-09-15 20:24:11, Oleg Nesterov wrote: > Both "child->mm == mm" and "p->mm != mm" checks in oom_kill_process() > are wrong. task->mm can be NULL if the task is the exited group leader. > This means in particular that "kill sharing same memory" loop can miss > a process with a zombie leader which uses the same ->mm. > > Note: the process_has_mm(child, p->mm) check is still not 100% correct, > p->mm can be NULL too. This is minor, but probably deserves a fix or a > comment anyway. > > Signed-off-by: Oleg Nesterov Acked-by: Michal Hocko > --- > mm/oom_kill.c | 16 ++++++++++++++-- > 1 file changed, 14 insertions(+), 2 deletions(-) > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > index c189ee5..034d219 100644 > --- a/mm/oom_kill.c > +++ b/mm/oom_kill.c > @@ -483,6 +483,18 @@ void oom_killer_enable(void) > oom_killer_disabled = false; > } > > +static bool process_shares_mm(struct task_struct *p, struct mm_struct *mm) > +{ > + struct task_struct *t; > + > + for_each_thread(p, t) { > + struct mm_struct *t_mm = READ_ONCE(t->mm); > + if (t_mm) > + return t_mm == mm; > + } > + return false; > +} > + > #define K(x) ((x) << (PAGE_SHIFT-10)) > /* > * Must be called while holding a reference to p, which will be released upon > @@ -530,7 +542,7 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p, > list_for_each_entry(child, &t->children, sibling) { > unsigned int child_points; > > - if (child->mm == p->mm) > + if (process_shares_mm(child, p->mm)) > continue; > /* > * oom_badness() returns 0 if the thread is unkillable > @@ -584,7 +596,7 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p, > */ > rcu_read_lock(); > for_each_process(p) { > - if (p->mm != mm) > + if (!process_shares_mm(p, mm)) > continue; > if (same_thread_group(p, victim)) > continue; > -- > 2.4.3 -- Michal Hocko SUSE Labs