From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752577AbcFPGYj (ORCPT ); Thu, 16 Jun 2016 02:24:39 -0400 Received: from mail-wm0-f65.google.com ([74.125.82.65]:35547 "EHLO mail-wm0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751490AbcFPGYh (ORCPT ); Thu, 16 Jun 2016 02:24:37 -0400 Date: Thu, 16 Jun 2016 08:24:34 +0200 From: Michal Hocko To: Oleg Nesterov Cc: linux-mm@kvack.org, Tetsuo Handa , David Rientjes , Vladimir Davydov , Andrew Morton , LKML Subject: Re: [PATCH 05/10] mm, oom: skip vforked tasks from being selected Message-ID: <20160616062433.GA30768@dhcp22.suse.cz> References: <1465473137-22531-1-git-send-email-mhocko@kernel.org> <1465473137-22531-6-git-send-email-mhocko@kernel.org> <20160615145106.GC7944@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160615145106.GC7944@redhat.com> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 15-06-16 16:51:06, Oleg Nesterov wrote: > On 06/09, Michal Hocko wrote: > > > > --- a/include/linux/sched.h > > +++ b/include/linux/sched.h > > @@ -1883,6 +1883,32 @@ extern int arch_task_struct_size __read_mostly; > > #define TNF_FAULT_LOCAL 0x08 > > #define TNF_MIGRATE_FAIL 0x10 > > > > +static inline bool in_vfork(struct task_struct *tsk) > > +{ > > + bool ret; > > + > > + /* > > + * need RCU to access ->real_parent if CLONE_VM was used along with > > + * CLONE_PARENT. > > + * > > + * We check real_parent->mm == tsk->mm because CLONE_VFORK does not > > + * imply CLONE_VM > > + * > > + * CLONE_VFORK can be used with CLONE_PARENT/CLONE_THREAD and thus > > + * ->real_parent is not necessarily the task doing vfork(), so in > > + * theory we can't rely on task_lock() if we want to dereference it. > > + * > > + * And in this case we can't trust the real_parent->mm == tsk->mm > > + * check, it can be false negative. But we do not care, if init or > > + * another oom-unkillable task does this it should blame itself. > > + */ > > + rcu_read_lock(); > > + ret = tsk->vfork_done && tsk->real_parent->mm == tsk->mm; > > + rcu_read_unlock(); > > + > > + return ret; > > +} > > ACK, but why sched.h ? It has a single caller in oom_kill.c. It felt like generally reusable helper to get subtle details about the vfork right. -- Michal Hocko SUSE Labs