From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from g4t3427.houston.hp.com ([15.201.208.55]:41917 "EHLO g4t3427.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753688AbaFRXTg (ORCPT ); Wed, 18 Jun 2014 19:19:36 -0400 Message-ID: <53A21E84.2050103@hp.com> Date: Wed, 18 Jun 2014 19:19:32 -0400 From: Waiman Long MIME-Version: 1.0 To: Josef Bacik CC: Marc Dionne , linux-btrfs@vger.kernel.org, clm@fb.com, t-itoh@jp.fujitsu.com Subject: Re: Lockups with btrfs on 3.16-rc1 - bisected References: <53A20FFF.3010807@hp.com> <53A2125B.3050701@fb.com> <53A21702.8090109@hp.com> <53A21C78.1040809@fb.com> In-Reply-To: <53A21C78.1040809@fb.com> Content-Type: text/plain; charset=UTF-8; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: On 06/18/2014 07:10 PM, Josef Bacik wrote: > > > On 06/18/2014 03:47 PM, Waiman Long wrote: >> On 06/18/2014 06:27 PM, Josef Bacik wrote: >>> >>> >>> On 06/18/2014 03:17 PM, Waiman Long wrote: >>>> On 06/18/2014 04:57 PM, Marc Dionne wrote: >>>>> Hi, >>>>> >>>>> I've been seeing very reproducible soft lockups with 3.16-rc1 similar >>>>> to what is reported here: >>>>> https://urldefense.proofpoint.com/v1/url?u=http://marc.info/?l%3Dlinux-btrfs%26m%3D140290088532203%26w%3D2&k=ZVNjlDMF0FElm4dQtryO4A%3D%3D%0A&r=cKCbChRKsMpTX8ybrSkonQ%3D%3D%0A&m=aoagvtZMwVb16gh1HApZZL00I7eP50GurBpuEo3l%2B5g%3D%0A&s=c62558feb60a480bbb52802093de8c97b5e1f23d4100265b6120c8065bd99565 >>>>> >>>>> >>>>> , along with the >>>>> occasional hard lockup, making it impossible to complete a parallel >>>>> build on a btrfs filesystem for the package I work on. This was >>>>> working fine just a few days before rc1. >>>>> >>>>> Bisecting brought me to the following commit: >>>>> >>>>> commit bd01ec1a13f9a327950c8e3080096446c7804753 >>>>> Author: Waiman Long >>>>> Date: Mon Feb 3 13:18:57 2014 +0100 >>>>> >>>>> x86, locking/rwlocks: Enable qrwlocks on x86 >>>>> >>>>> And sure enough if I revert that commit on top of current mainline, >>>>> I'm unable to reproduce the soft lockups and hangs. >>>>> >>>>> Marc >>>> >>>> The queue rwlock is fair. As a result, recursive read_lock is not >>>> allowed unless the task is in an interrupt context. Doing recursive >>>> read_lock will hang the process when a write_lock happens somewhere in >>>> between. Are recursive read_lock being done in the btrfs code? >>>> >>> >>> We walk down a tree and read lock each node as we walk down, is that >>> what you mean? Or do you mean read_lock multiple times on the same >>> lock in the same process, cause we definitely don't do that. Thanks, >>> >>> Josef >> >> I meant recursively read_lock the same lock in a process. > > I take it back, we do actually do this in some cases. Thanks, > > Josef This is what I thought when I looked at the looking code in btrfs. The unlock code doesn't clear the lock_owner pid, this may cause the lock_nested to be set incorrectly. Anyway, are you going to do something about it? -Longman