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[195.250.132.146]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-32549fe6c74sm10082400a91.6.2025.08.26.07.14.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 26 Aug 2025 07:14:57 -0700 (PDT) Date: Tue, 26 Aug 2025 16:14:47 +0200 From: Michal =?utf-8?Q?Koutn=C3=BD?= To: Chen Ridong Cc: tj@kernel.org, hannes@cmpxchg.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, lujialin4@huawei.com, chenridong@huawei.com Subject: Re: [PATCH cgroup/for-next 1/3] cgroup: remove redundancy online_cnt Message-ID: References: <20250826034022.1736249-1-chenridong@huaweicloud.com> <20250826034022.1736249-2-chenridong@huaweicloud.com> Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="e37cwfg4njgbpo5x" Content-Disposition: inline In-Reply-To: <20250826034022.1736249-2-chenridong@huaweicloud.com> --e37cwfg4njgbpo5x Content-Type: text/plain; protected-headers=v1; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Subject: Re: [PATCH cgroup/for-next 1/3] cgroup: remove redundancy online_cnt MIME-Version: 1.0 Hello Ridong. On Tue, Aug 26, 2025 at 03:40:20AM +0000, Chen Ridong wrote: > @@ -5949,7 +5944,7 @@ static void css_killed_work_fn(struct work_struct *= work) > css_put(css); > /* @css can't go away while we're holding cgroup_mutex */ > css =3D css->parent; > - } while (css && atomic_dec_and_test(&css->online_cnt)); > + } while (css && css_is_dying(css) && !css->nr_descendants); Here it's OK... > =20 > cgroup_unlock(); > } > @@ -5960,7 +5955,7 @@ static void css_killed_ref_fn(struct percpu_ref *re= f) > struct cgroup_subsys_state *css =3D > container_of(ref, struct cgroup_subsys_state, refcnt); > =20 > - if (atomic_dec_and_test(&css->online_cnt)) { > + if (!css->nr_descendants) { > INIT_WORK(&css->destroy_work, css_killed_work_fn); > queue_work(cgroup_offline_wq, &css->destroy_work); > } =2E.. but here in percpu_ref's confirm callback you're accessing nr_descendants without cgroup_mutex where the atomic would have prevented the data race. Also the semantics of online_cnt and nr_descendants is slightly different -- killed vs offlined. Or can you add a description why they're same (after workqueue split)? Thanks, Michal --e37cwfg4njgbpo5x Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iJEEABYKADkWIQRCE24Fn/AcRjnLivR+PQLnlNv4CAUCaK3BVRsUgAAAAAAEAA5t YW51MiwyLjUrMS4xMSwyLDIACgkQfj0C55Tb+AhMrAD9HaLehNCEvy9tY5TFCzK1 fhYL1r/LBmh6LZ69zkiz/coBALFvZYfRRnQz7gf8u6NLbLjSunueITfmuykfyiWJ k6QB =V09U -----END PGP SIGNATURE----- --e37cwfg4njgbpo5x--