From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f53.google.com (mail-wm0-f53.google.com [74.125.82.53]) by kanga.kvack.org (Postfix) with ESMTP id C32A1828F3 for ; Sun, 10 Jan 2016 15:39:09 -0500 (EST) Received: by mail-wm0-f53.google.com with SMTP id b14so241157771wmb.1 for ; Sun, 10 Jan 2016 12:39:09 -0800 (PST) Received: from mail-wm0-x230.google.com (mail-wm0-x230.google.com. [2a00:1450:400c:c09::230]) by mx.google.com with ESMTPS id 75si17477753wmn.68.2016.01.10.12.39.08 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 10 Jan 2016 12:39:08 -0800 (PST) Received: by mail-wm0-x230.google.com with SMTP id b14so241157469wmb.1 for ; Sun, 10 Jan 2016 12:39:08 -0800 (PST) Date: Sun, 10 Jan 2016 22:39:06 +0200 From: "Kirill A. Shutemov" Subject: Re: mm: possible deadlock in mm_take_all_locks Message-ID: <20160110203906.GA16888@node.shutemov.name> References: <20160108232352.GA13046@node.shutemov.name> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Dmitry Vyukov Cc: Michal Hocko , Peter Zijlstra , Ingo Molnar , LKML , Andrew Morton , "Kirill A. Shutemov" , Oleg Nesterov , Chen Gang , "linux-mm@kvack.org" , syzkaller , Kostya Serebryany , Alexander Potapenko , Eric Dumazet , Sasha Levin On Sun, Jan 10, 2016 at 09:05:32AM +0100, Dmitry Vyukov wrote: > On Sat, Jan 9, 2016 at 12:23 AM, Kirill A. Shutemov > wrote: > > On Fri, Jan 08, 2016 at 05:58:33PM +0100, Dmitry Vyukov wrote: > >> Hello, > >> > >> I've hit the following deadlock warning while running syzkaller fuzzer > >> on commit b06f3a168cdcd80026276898fd1fee443ef25743. As far as I > >> understand this is a false positive, because both call stacks are > >> protected by mm_all_locks_mutex. > > > > +Michal > > > > I don't think it's false positive. > > > > The reason we don't care about order of taking i_mmap_rwsem is that we > > never takes i_mmap_rwsem under other i_mmap_rwsem, but that's not true for > > i_mmap_rwsem vs. hugetlbfs_i_mmap_rwsem_key. That's why we have the > > annotation in the first place. > > > > See commit b610ded71918 ("hugetlb: fix lockdep splat caused by pmd > > sharing"). > > Description of b610ded71918 suggests that that code takes hugetlb > mutex first and them normal page mutex. In this patch you take them in > the opposite order: normal mutex, then hugetlb mutex. Won't this patch > only increase probability of deadlocks? Shouldn't you take them in the > opposite order? You are right. I got it wrong. Conditions should be reversed. The comment around hugetlbfs_i_mmap_rwsem_key definition is somewhat confusing: "This needs an annotation because huge_pmd_share() does an allocation under i_mmap_rwsem." I read this as we do hugetlb allocation when i_mmap_rwsem already taken and made locking order respectively. I guess i_mmap_rwsem should be replaced with hugetlbfs_i_mmap_rwsem_key in the comment. -- Kirill A. Shutemov -- 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