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Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.7.1 Subject: Re: [PATCH] blk-cgroup: Flush stats before releasing blkcg_gq Content-Language: en-US To: =?UTF-8?Q?Michal_Koutn=c3=bd?= , Ming Lei Cc: Yosry Ahmed , Linux-MM , Michal Hocko , Shakeel Butt , Johannes Weiner , Roman Gushchin , Muchun Song , Jens Axboe , linux-block@vger.kernel.org, cgroups@vger.kernel.org, Tejun Heo References: <20230524011935.719659-1-ming.lei@redhat.com> <3ej42djuuzwx36yf2yeo5ggyrvogeaguos5jtve2bvuaejnwff@fak3yjwe2fbi> From: Waiman Long In-Reply-To: <3ej42djuuzwx36yf2yeo5ggyrvogeaguos5jtve2bvuaejnwff@fak3yjwe2fbi> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 X-Stat-Signature: zgoyjhrd5o9wgj9iqpdt1sa7ym96g44a X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: DBB5940021 X-Rspam-User: X-HE-Tag: 1685028313-744243 X-HE-Meta: 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 MNKqBfBQ z8+FEOTsXHdgJjoWObgDk4+iAux9cfEhxg/oyYPx2pf2z31OVcl4ddsf9pIx0fqCrtaoL2niAolfEDk7m9BEqYgKKENur9vDj/FUeKgm4q8GaDQWG9pidZSShEq2UIqLVP3av6i6eea+5U9gU8Cf2BgCJ1RXrJynPQrzr/LFbFlCcjO1oWtsxsPreG/N86rak/xR6R1J73E8gpQwEsZTq5WmuPdZe3zz9ic14F8/Mr4GY0VEGtrOOqwK6Tkn9RJgendLy 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 5/25/23 10:11, Michal Koutný wrote: > On Wed, May 24, 2023 at 10:37:10AM +0800, Ming Lei wrote: >>> I am not at all familiar with blkcg, but does calling >>> cgroup_rstat_flush() in offline_css() fix the problem? >> Except for offline, this list needs to be flushed after the associated disk >> is deleted. > Why the second flush trigger? > a) To break another ref-dependency cycle (like on the blkcg side)? > b) To avoid stale data upon device removal? > > (Because b) should be unnecessary, a future reader would flush when > needed.) Since the percpu blkg_iostat_set's that are linked in the lockless list will be freed if the corresponding blkcg_gq is freed, we need to flush the lockless list to avoid potential use-after-free in a future cgroup_rstat_flush*() call. Cheers, Longman