From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0b-00082601.pphosted.com ([67.231.153.30]:53283 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1755733AbaFRXK4 (ORCPT ); Wed, 18 Jun 2014 19:10:56 -0400 Message-ID: <53A21C78.1040809@fb.com> Date: Wed, 18 Jun 2014 16:10:48 -0700 From: Josef Bacik MIME-Version: 1.0 To: Waiman Long CC: Marc Dionne , , , Subject: Re: Lockups with btrfs on 3.16-rc1 - bisected References: <53A20FFF.3010807@hp.com> <53A2125B.3050701@fb.com> <53A21702.8090109@hp.com> In-Reply-To: <53A21702.8090109@hp.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: 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