From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f70.google.com (mail-wm0-f70.google.com [74.125.82.70]) by kanga.kvack.org (Postfix) with ESMTP id 952EC6B03B4 for ; Fri, 11 Aug 2017 03:09:42 -0400 (EDT) Received: by mail-wm0-f70.google.com with SMTP id a186so5369163wmh.9 for ; Fri, 11 Aug 2017 00:09:42 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id c28si188762wra.29.2017.08.11.00.09.40 for (version=TLS1 cipher=AES128-SHA bits=128/128); Fri, 11 Aug 2017 00:09:40 -0700 (PDT) Date: Fri, 11 Aug 2017 09:09:38 +0200 From: Michal Hocko Subject: Re: [PATCH 2/2] mm, oom: fix potential data corruption when oom_reaper races with writer Message-ID: <20170811070938.GA30811@dhcp22.suse.cz> References: <20170807113839.16695-1-mhocko@kernel.org> <20170807113839.16695-3-mhocko@kernel.org> <201708111128.FEE39036.HFVSQFOtOMLFJO@I-love.SAKURA.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201708111128.FEE39036.HFVSQFOtOMLFJO@I-love.SAKURA.ne.jp> Sender: owner-linux-mm@kvack.org List-ID: To: Tetsuo Handa Cc: akpm@linux-foundation.org, andrea@kernel.org, kirill@shutemov.name, oleg@redhat.com, wenwei.tww@alibaba-inc.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org On Fri 11-08-17 11:28:52, Tetsuo Handa wrote: > Michal Hocko wrote: > > +/* > > + * Checks whether a page fault on the given mm is still reliable. > > + * This is no longer true if the oom reaper started to reap the > > + * address space which is reflected by MMF_UNSTABLE flag set in > > + * the mm. At that moment any !shared mapping would lose the content > > + * and could cause a memory corruption (zero pages instead of the > > + * original content). > > + * > > + * User should call this before establishing a page table entry for > > + * a !shared mapping and under the proper page table lock. > > + * > > + * Return 0 when the PF is safe VM_FAULT_SIGBUS otherwise. > > + */ > > +static inline int check_stable_address_space(struct mm_struct *mm) > > +{ > > + if (unlikely(test_bit(MMF_UNSTABLE, &mm->flags))) > > + return VM_FAULT_SIGBUS; > > + return 0; > > +} > > + > > Will you explain the mechanism why random values are written instead of zeros > so that this patch can actually fix the race problem? I am not sure what you mean here. Were you able to see a write with an unexpected content? -- Michal Hocko SUSE Labs -- 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/ . Don't email: email@kvack.org