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Mon, 07 Jul 2025 02:23:51 -0700 (PDT) Received: from blackdock.suse.cz ([193.86.92.181]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-454b1698e24sm105561945e9.34.2025.07.07.02.23.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 07 Jul 2025 02:23:50 -0700 (PDT) Date: Mon, 7 Jul 2025 11:23:49 +0200 From: Michal =?utf-8?Q?Koutn=C3=BD?= To: Shakeel Butt Cc: Tejun Heo , "Paul E . McKenney" , Andrew Morton , JP Kobryn , Johannes Weiner , Ying Huang , Vlastimil Babka , Alexei Starovoitov , Sebastian Andrzej Siewior , bpf@vger.kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Meta kernel team Subject: Re: [PATCH v3] cgroup: llist: avoid memory tears for llist_node Message-ID: <6isu4w3ri66t7kli43hpw4mehjvhipzndktbxrar3ttccap6jy@q2f2xdimxpga> References: <20250704180804.3598503-1-shakeel.butt@linux.dev> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="gsl2hznmnpg6a4vg" Content-Disposition: inline In-Reply-To: <20250704180804.3598503-1-shakeel.butt@linux.dev> X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 1FF6F14000A X-Stat-Signature: i9fk7gmi96s9aykk35b7qdhymubpkgjb X-Rspam-User: X-HE-Tag: 1751880232-66979 X-HE-Meta: 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 Xw9gXKME 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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: List-Subscribe: List-Unsubscribe: --gsl2hznmnpg6a4vg Content-Type: text/plain; protected-headers=v1; charset=us-ascii Content-Disposition: inline Subject: Re: [PATCH v3] cgroup: llist: avoid memory tears for llist_node MIME-Version: 1.0 On Fri, Jul 04, 2025 at 11:08:04AM -0700, Shakeel Butt wrote: > More specifically the rstat updater and the flusher can race and cause > a scenario where the stats updater skips adding the css to the > lockless list but the flusher might not see those updates done by the > skipped updater. This is benign race and the subsequent flusher will > flush those stats and at the moment there aren't any rstat users which > are not fine with this kind of race. Yes, the updaters and flushers has always been in a race. > However some future user might want more stricter guarantee, so let's > add appropriate comments to ease the job of future users. I believe there should never be such (external) users as updaters shouldn't be excluded by flushers in principle. (There is the exclusion for bookkeeping the updated tree paths correctly though.) So, thanks for the comments, one should be wary of them when considering the update updated subtree. Michal --gsl2hznmnpg6a4vg Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYKAB0WIQRCE24Fn/AcRjnLivR+PQLnlNv4CAUCaGuSIgAKCRB+PQLnlNv4 CI7wAP4u/qgZyNwgTwsnKQhklrdWHI6kyPoLqOFcM+dj1w9SpwD+IdhdgkfQ/WaU LR0OIEBPOfWPYJAbpSSCgzEVBHFm8gc= =Rpm6 -----END PGP SIGNATURE----- --gsl2hznmnpg6a4vg--