From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f45.google.com (mail-wm0-f45.google.com [74.125.82.45]) by kanga.kvack.org (Postfix) with ESMTP id 7ED8F828F3 for ; Mon, 11 Jan 2016 04:04:46 -0500 (EST) Received: by mail-wm0-f45.google.com with SMTP id f206so203856942wmf.0 for ; Mon, 11 Jan 2016 01:04:46 -0800 (PST) Received: from mail-wm0-x22d.google.com (mail-wm0-x22d.google.com. [2a00:1450:400c:c09::22d]) by mx.google.com with ESMTPS id br5si104461211wjb.69.2016.01.11.01.04.45 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 11 Jan 2016 01:04:45 -0800 (PST) Received: by mail-wm0-x22d.google.com with SMTP id l65so202077602wmf.1 for ; Mon, 11 Jan 2016 01:04:45 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20160110203906.GA16888@node.shutemov.name> References: <20160108232352.GA13046@node.shutemov.name> <20160110203906.GA16888@node.shutemov.name> From: Dmitry Vyukov Date: Mon, 11 Jan 2016 10:04:25 +0100 Message-ID: Subject: Re: mm: possible deadlock in mm_take_all_locks Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: "Kirill A. Shutemov" 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 9:39 PM, Kirill A. Shutemov wrote: > 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. Comment on mm_take_all_locks probably also needs updating. -- 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