From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752525Ab1GaUUf (ORCPT ); Sun, 31 Jul 2011 16:20:35 -0400 Received: from mx1.fusionio.com ([66.114.96.30]:56438 "EHLO mx1.fusionio.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752289Ab1GaUU2 (ORCPT ); Sun, 31 Jul 2011 16:20:28 -0400 X-ASG-Debug-ID: 1312143627-03d6a510aa2128d0001-xx1T2L X-Barracuda-Envelope-From: JAxboe@fusionio.com Message-ID: <4E35B908.6090507@fusionio.com> Date: Sun, 31 Jul 2011 22:20:24 +0200 From: Jens Axboe MIME-Version: 1.0 To: Kay Sievers CC: Milan Broz , Tejun Heo , "linux-kernel@vger.kernel.org" Subject: Re: loop: fix deadlock when sysfs and LOOP_CLR_FD race against each other References: <1312053553.1187.17.camel@mop> X-ASG-Orig-Subj: Re: loop: fix deadlock when sysfs and LOOP_CLR_FD race against each other In-Reply-To: <1312053553.1187.17.camel@mop> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-Barracuda-Connect: mail1.int.fusionio.com[10.101.1.21] X-Barracuda-Start-Time: 1312143627 X-Barracuda-URL: http://10.101.1.180:8000/cgi-mod/mark.cgi X-Barracuda-Spam-Score: 0.00 X-Barracuda-Spam-Status: No, SCORE=0.00 using per-user scores of TAG_LEVEL=1000.0 QUARANTINE_LEVEL=1000.0 KILL_LEVEL=9.0 tests= X-Barracuda-Spam-Report: Code version 3.2, rules version 3.2.2.70528 Rule breakdown below pts rule name description ---- ---------------------- -------------------------------------------------- Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2011-07-30 21:19, Kay Sievers wrote: > From: Kay Sievers > Subject: loop: fix deadlock when sysfs and LOOP_CLR_FD race against each other > > LOOP_CLR_FD takes lo->lo_ctl_mutex and tries to remove the loop sysfs > files. Sysfs calls show() and waits for lo->lo_ctl_mutex. LOOP_CLR_FD > waits for show() to finish to remove the sysfs file. > > cat /sys/class/block/loop0/loop/backing_file > mutex_lock_nested+0x176/0x350 > ? loop_attr_do_show_backing_file+0x2f/0xd0 [loop] > ? loop_attr_do_show_backing_file+0x2f/0xd0 [loop] > loop_attr_do_show_backing_file+0x2f/0xd0 [loop] > dev_attr_show+0x1b/0x60 > ? sysfs_read_file+0x86/0x1a0 > ? __get_free_pages+0x12/0x50 > sysfs_read_file+0xaf/0x1a0 > > ioctl(LOOP_CLR_FD): > wait_for_common+0x12c/0x180 > ? try_to_wake_up+0x2a0/0x2a0 > wait_for_completion+0x18/0x20 > sysfs_deactivate+0x178/0x180 > ? sysfs_addrm_finish+0x43/0x70 > ? sysfs_addrm_start+0x1d/0x20 > sysfs_addrm_finish+0x43/0x70 > sysfs_hash_and_remove+0x85/0xa0 > sysfs_remove_group+0x59/0x100 > loop_clr_fd+0x1dc/0x3f0 [loop] > lo_ioctl+0x223/0x7a0 [loop] > > Instead of taking the lo_ctl_mutex from sysfs code, take the inner > lo->lo_lock, to protect the access to the backing_file data. > > Thanks to Tejun for help debugging and finding a solution. Looks good, looks like something that should have a stable tag as well? -- Jens Axboe