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From: Shakeel Butt Date: Mon, 21 Apr 2025 21:41:13 -0700 X-Gmail-Original-Message-ID: X-Gm-Features: ATxdqUHGnbKtYzS7_6xMY77prDcfzTNXx7RPZ1T_ZR4If9HzihBdR3-O4dlMnlA Message-ID: Subject: Re: [PATCH] cpuset: relax locking on cpuset_node_allowed To: Gregory Price Cc: linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, longman@redhat.com, hannes@cmpxchg.org, mhocko@kernel.org, roman.gushchin@linux.dev, muchun.song@linux.dev, tj@kernel.org, mkoutny@suse.com, akpm@linux-foundation.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Queue-Id: 48885100006 X-Rspamd-Server: rspam04 X-Stat-Signature: 334dgetnpin81yn9zbkmdcpyta6rnszj X-HE-Tag: 1745296898-371268 X-HE-Meta: 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 aSqx/1Lt W58sSJULLt1MX2Wx21ci4kO7KjKgiEdxqMK++I/r6FPjC2MAQ8a6LHTbXU1nSjqPeCdHtZd5dx7kddn/xrLt9Hndczhjd0LtYnDJnEZPHM1/OVBApNqv38N6Z7RmXvdXiQqXWovQO6hGq/p6ZNkyydQafe6ndWzD6iUF0Fgb1ZBAd4PD5Akd79kQq2SamVYxfS17GVhC+zLXJkUYJP7ZHpsejadBmRD2QGYzHpdUlTn9lr8pLm92O6RJgFc35/3qiAR9g3yRi8vbzEZkikTORfn2WAEwaBTkz95IdaqNpTBnYIM8= 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 Mon, Apr 21, 2025 at 9:30=E2=80=AFPM Gregory Price w= rote: > > The cgroup_get_e_css reference protects the css->effective_mems, and > calls of this interface would be subject to the same race conditions > associated with a non-atomic access to cs->effective_mems. > > So while this interface cannot make strong guarantees of correctness, > it can therefore avoid taking a global or rcu_read_lock for performance. > > Drop the rcu_read_lock from cpuset_node_allowed. > > Suggested-by: Shakeel Butt > Suggested-by: Waiman Long > Signed-off-by: Gregory Price Reviewed-by: Shakeel Butt