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Wed, 20 Mar 2024 17:38:40 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id oStwJyAf+2V5fwAAD6G6ig (envelope-from ); Wed, 20 Mar 2024 17:38:40 +0000 Date: Wed, 20 Mar 2024 18:38:31 +0100 From: Michal Hocko To: Waiman Long Cc: Pavel Tikhomirov , Johannes Weiner , Roman Gushchin , Shakeel Butt , Muchun Song , Andrew Morton , Vladimir Davydov , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel@openvz.org Subject: Re: [PATCH] mm/memcontrol: stop resize loop if limit was changed again Message-ID: References: <20240320100556.463266-1-ptikhomirov@virtuozzo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Spamd-Bar: / X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 2F4B01C0016 X-Stat-Signature: 7rejdzxs67dio7qepoq8go6y8b9ntgsi X-Rspam-User: X-HE-Tag: 1710956322-962074 X-HE-Meta: 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 mrA== 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: List-Subscribe: List-Unsubscribe: On Wed 20-03-24 18:12:50, Michal Hocko wrote: > On Wed 20-03-24 13:09:07, Waiman Long wrote: > > > > On 3/20/24 06:03, Pavel Tikhomirov wrote: > > > In memory_max_write() we first set memcg->memory.max and only then > > > try to enforce it in loop. What if while we are in loop someone else > > > have changed memcg->memory.max but we are still trying to enforce > > > the old value? I believe this can lead to nasty consequence like getting > > > an oom on perfectly fine cgroup within it's limits or excess reclaim. > > > > Concurrent write to the same cgroup control file is not possible as the > > underlying kernfs_open_file structure has a mutex that serialize access to > > the file. > > This is good to know and I was not aware of that. Thanks! Btw. even if the interface itself is serialized then uncoordinated userspace is still timing dependent so fundamentally racy. -- Michal Hocko SUSE Labs