From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751710AbcBCKkU (ORCPT ); Wed, 3 Feb 2016 05:40:20 -0500 Received: from mail-wm0-f49.google.com ([74.125.82.49]:34465 "EHLO mail-wm0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750741AbcBCKkQ (ORCPT ); Wed, 3 Feb 2016 05:40:16 -0500 Subject: Re: [PATCH 1/4] block: fix module reference leak on put_disk() call for cgroups throttle To: Roman Pen References: <1454338315-13465-1-git-send-email-roman.penyaev@profitbricks.com> <1454338315-13465-2-git-send-email-roman.penyaev@profitbricks.com> Cc: Tejun Heo , Jens Axboe , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org From: Gi-Oh Kim Message-ID: <56B1D90D.9040502@profitbricks.com> Date: Wed, 3 Feb 2016 11:40:13 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1 MIME-Version: 1.0 In-Reply-To: <1454338315-13465-2-git-send-email-roman.penyaev@profitbricks.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01.02.2016 15:51, Roman Pen wrote: > get_disk(),get_gendisk() calls have non explicit side effect: they > increase the reference on the disk owner module. > > The following is the correct sequence how to get a disk reference and > to put it: > > disk = get_gendisk(...); > > /* use disk */ > > owner = disk->fops->owner; > put_disk(disk); > module_put(owner); > > fs/block_dev.c is aware of this required module_put() call, but f.e. > blkg_conf_finish(), which is located in block/blk-cgroup.c, does not put > a module reference. To see a leakage in action cgroups throttle config > can be used. In the following script I'm removing throttle for /dev/ram0 > (actually this is NOP, because throttle was never set for this device): > > # lsmod | grep brd > brd 5175 0 > # i=100; while [ $i -gt 0 ]; do echo "1:0 0" > \ > /sys/fs/cgroup/blkio/blkio.throttle.read_bps_device; i=$(($i - 1)); \ > done > # lsmod | grep brd > brd 5175 100 > > Now brd module has 100 references. I hope this patch would be merged into stable versions. I've tested the patch with v3.12.45 on my server. Before apply the patch, reference count was leaked. # lsmod | grep loop loop 16091 0 # echo "7:0 1048576" > /sys/fs/cgroup/blkio/blkio.throttle.read_bps_device # lsmod | grep loop loop 16091 1 # echo "7:0 1048576" > /sys/fs/cgroup/blkio/blkio.throttle.read_bps_device # lsmod | grep loop loop 16091 2 # echo "7:0 1048576" > /sys/fs/cgroup/blkio/blkio.throttle.read_bps_device # lsmod | grep loop loop 16091 3 # echo "7:0 1048576" > /sys/fs/cgroup/blkio/blkio.throttle.read_bps_device # lsmod | grep loop loop 16091 4 After apply the patch, reference count was still: # lsmod | grep loop loop 19171 0 # echo "7:0 1048576" > /sys/fs/cgroup/blkio/blkio.throttle.read_bps_device # lsmod | grep loop loop 19171 0 # echo "7:0 1048576" > /sys/fs/cgroup/blkio/blkio.throttle.read_bps_device # lsmod | grep loop loop 19171 0 # echo "7:0 1048576" > /sys/fs/cgroup/blkio/blkio.throttle.read_bps_device # lsmod | grep loop loop 19171 0 -- Best regards, Gi-Oh Kim