From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0b-00082601.pphosted.com ([67.231.153.30]:30161 "EHLO mx0b-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752463AbaFRW1w (ORCPT ); Wed, 18 Jun 2014 18:27:52 -0400 Message-ID: <53A2125B.3050701@fb.com> Date: Wed, 18 Jun 2014 15:27:39 -0700 From: Josef Bacik MIME-Version: 1.0 To: Waiman Long , Marc Dionne CC: , , Subject: Re: Lockups with btrfs on 3.16-rc1 - bisected References: <53A20FFF.3010807@hp.com> In-Reply-To: <53A20FFF.3010807@hp.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: On 06/18/2014 03:17 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