From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wg0-f41.google.com (mail-wg0-f41.google.com [74.125.82.41]) by kanga.kvack.org (Postfix) with ESMTP id EEE2C900002 for ; Fri, 11 Jul 2014 04:33:29 -0400 (EDT) Received: by mail-wg0-f41.google.com with SMTP id z12so681838wgg.12 for ; Fri, 11 Jul 2014 01:33:28 -0700 (PDT) Received: from mx2.suse.de (cantor2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id j4si2820735wja.141.2014.07.11.01.33.20 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Fri, 11 Jul 2014 01:33:20 -0700 (PDT) Message-ID: <53BFA14B.4010203@suse.cz> Date: Fri, 11 Jul 2014 10:33:15 +0200 From: Vlastimil Babka MIME-Version: 1.0 Subject: Re: + shmem-fix-faulting-into-a-hole-while-its-punched-take-2.patch added to -mm tree References: <53BD1053.5020401@suse.cz> <53BD39FC.7040205@oracle.com> <53BD67DC.9040700@oracle.com> <53BE8B1B.3000808@oracle.com> <53BECBA4.3010508@oracle.com> <53BED7F6.4090502@oracle.com> <53BEE345.4090203@oracle.com> <20140711082500.GB20603@laptop.programming.kicks-ass.net> In-Reply-To: <20140711082500.GB20603@laptop.programming.kicks-ass.net> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Peter Zijlstra , Sasha Levin Cc: Hugh Dickins , Heiko Carstens , akpm@linux-foundation.org, davej@redhat.com, koct9i@gmail.com, lczerner@redhat.com, stable@vger.kernel.org, "linux-mm@kvack.org" , LKML On 07/11/2014 10:25 AM, Peter Zijlstra wrote: > On Thu, Jul 10, 2014 at 03:02:29PM -0400, Sasha Levin wrote: >> What if we move lockdep's acquisition point to after it actually got the >> lock? > > NAK, you want to do deadlock detection _before_ you're stuck in a > deadlock. > >> We'd miss deadlocks, but we don't care about them right now. Anyways, doesn't >> lockdep have anything built in to allow us to separate between locks which >> we attempt to acquire and locks that are actually acquired? >> >> (cc PeterZ) >> >> We can treat locks that are in the process of being acquired the same as >> acquired locks to avoid races, but when we print something out it would >> be nice to have annotation of the read state of the lock. > > I'm missing the problem here I think. Quoting Hugh from previous mail in this thread: >> > >> > [ 363.600969] INFO: task trinity-c327:9203 blocked for more than 120 seconds. >> > [ 363.605359] Not tainted 3.16.0-rc4-next-20140708-sasha-00022-g94c7290-dirty #772 >> > [ 363.609730] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. >> > [ 363.615861] trinity-c327 D 000000000000000b 13496 9203 8559 0x10000004 >> > [ 363.620284] ffff8800b857bce8 0000000000000002 ffffffff9dc11b10 0000000000000001 >> > [ 363.624468] ffff880104860000 ffff8800b857bfd8 00000000001d7740 00000000001d7740 >> > [ 363.629118] ffff880104863000 ffff880104860000 ffff8800b857bcd8 ffff8801eaed8868 >> > [ 363.633879] Call Trace: >> > [ 363.635442] [] schedule+0x65/0x70 >> > [ 363.638638] [] schedule_preempt_disabled+0x18/0x30 >> > [ 363.642833] [] mutex_lock_nested+0x2e5/0x550 >> > [ 363.646599] [] ? shmem_fallocate+0x6c/0x350 >> > [ 363.651319] [] ? get_parent_ip+0x11/0x50 >> > [ 363.654683] [] ? shmem_fallocate+0x6c/0x350 >> > [ 363.658264] [] shmem_fallocate+0x6c/0x350 > > So it's trying to acquire i_mutex at shmem_fallocate+0x6c... > >> > [ 363.662010] [] ? put_lock_stats.isra.12+0xe/0x30 >> > [ 363.665866] [] do_fallocate+0x153/0x1d0 >> > [ 363.669381] [] SyS_madvise+0x33f/0x970 >> > [ 363.672906] [] tracesys+0xe1/0xe6 >> > [ 363.682900] 2 locks held by trinity-c327/9203: >> > [ 363.684928] #0: (sb_writers#12){.+.+.+}, at: [] do_fallocate+0x13d/0x1d0 >> > [ 363.715102] #1: (&sb->s_type->i_mutex_key#16){+.+.+.}, at: [] shmem_fallocate+0x6c/0x350 > > ...but it already holds i_mutex, acquired at shmem_fallocate+0x6c. > Am I reading that correctly? The output looks like mutex #1 is already taken, but actually the process is sleeping when trying to take it. It appears that the output has taken mutex_acquire_nest() action into account, but doesn't distinguish if lock_acquired() already happened or not. -- 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