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[2603:800c:1a02:1bae:a7fa:157f:969a:4cde]) by smtp.gmail.com with ESMTPSA id z29-20020aa7991d000000b00575afe3c188sm6255061pff.150.2022.12.12.14.13.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 12 Dec 2022 14:13:48 -0800 (PST) Date: Mon, 12 Dec 2022 12:13:47 -1000 From: Tejun Heo To: Waiman Long 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, Michal =?iso-8859-1?Q?Koutn=FD?= , "Dennis Zhou (Facebook)" , Yi Zhang Subject: Re: [PATCH-block v2 1/3] bdi, blk-cgroup: Fix potential UAF of blkcg Message-ID: References: <20221211222058.2946830-1-longman@redhat.com> <20221211222058.2946830-2-longman@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221211222058.2946830-2-longman@redhat.com> X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: B588A140004 X-Stat-Signature: n6z5h7qba5egp4hrpny4zxsxqrp6ecu6 X-Rspam-User: X-HE-Tag: 1670883230-939899 X-HE-Meta: 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 k8Jo/1zO AFNv32o9D8zzS9p/aRvXjMXahJDCWiA2/1Ul7daQpzRD/jEmVKBJEiq5svR1VorZ/h0ccD6JuRYeMPQjuUzXf3rA3RpY7ETa9LA8DNPPsuj9C0oWill7sIu1EOe7XOo03Nb4s9ctgej2tmpoJktK1TV705DGRWUYpu7bgd0nhCRAHbmnYrheEtlqHaNpGay1FkY1/JRgQTQSuw0CvinBwuycGBs1HDxEHjUQ2h2MeHdh0ouK6f99Y1/cF4g== 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 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? Thanks. -- tejun