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Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.4.0 Subject: Re: [PATCH-block v2 1/3] bdi, blk-cgroup: Fix potential UAF of blkcg Content-Language: en-US To: Tejun Heo Cc: Jens Axboe , Josef Bacik , Zefan Li , Johannes Weiner , Andrew Morton , cgroups@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, =?UTF-8?Q?Michal_Koutn=c3=bd?= , "Dennis Zhou (Facebook)" , Yi Zhang References: <20221211222058.2946830-1-longman@redhat.com> <20221211222058.2946830-2-longman@redhat.com> From: Waiman Long In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 36CE980002 X-Stat-Signature: 4at9obw9hgtkw79yqxc6ers6rxn6ixon X-HE-Tag: 1670883410-813591 X-HE-Meta: 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 12/12/22 17:13, Tejun Heo wrote: > On Sun, Dec 11, 2022 at 05:20:56PM -0500, Waiman Long wrote: >> static void blkcg_destroy_blkgs(struct blkcg *blkcg) >> { >> + /* >> + * blkcg_destroy_blkgs() shouldn't be called with all the blkcg >> + * references gone. >> + */ >> + if (WARN_ON_ONCE(!css_tryget(&blkcg->css))) >> + return; > Wouldn't it make more sense to use percpu_ref_is_zero()? It's not like the > obtained extra reference does anything, right? Yes, that makes sense. Will incorporate the change in the next version. Thanks, Longman