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b=QodwpJl8LgA0tAs/Ed4XU6lKjkVzRkPVTn1mvkR2m700vx+dg/C36CMq5EA430M8j NFeO6/Xy2OpKGxh1br3FuHqcjlxhm4YjqqjYErMdYpUEcrYss0BHlgCklJoyJWmHV8 9ClCI0kaA6W4SSO1tML+maH2YGRDO4KUh/IlOcXE= Date: Mon, 22 Sep 2025 16:55:09 -0700 From: Andrew Morton To: Shakeel Butt Cc: Tejun Heo , Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Alexei Starovoitov , Peilin Ye , Kumar Kartikeya Dwivedi , bpf@vger.kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Meta kernel team , Michal Hocko Subject: Re: [PATCH v2] memcg: skip cgroup_file_notify if spinning is not allowed Message-Id: <20250922165509.3fe07892054bb9e149e7cc06@linux-foundation.org> In-Reply-To: <552lz3qxc3z45r446rfndi7gx6nsht5iuhrhaszljofka2zrfs@odxfnm2blgdd> References: <20250922220203.261714-1-shakeel.butt@linux.dev> <20250922160443.f48bb14e2d055e6e954cd874@linux-foundation.org> <552lz3qxc3z45r446rfndi7gx6nsht5iuhrhaszljofka2zrfs@odxfnm2blgdd> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 48EDD80008 X-Rspamd-Server: rspam05 X-Stat-Signature: dwi6ee47d17xdh3g74j79ezjdjbaf1hg X-Rspam-User: X-HE-Tag: 1758585312-889973 X-HE-Meta: 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 nhDVtSuM ZWE1EqYlCTXESU0wB8zwE53dRLAW7PNPO8KjfIZG1km09c2jWOEB+ZPdLQ4q3DpqOJ+SzUdamnaj1/YV00yOOFOjUPRSE+ZUlFCnLfKNT9pLyI4iLCOc6F25Jr8Z9zUPmzaUatvfKcyfSB8ooT5aDqTqh2evaCTQpG46n8v7KdtplxQz9iqHARGqr186Yns7U28ZkseGd67zZ3yNzhsoL3l2gM+YrZ6uvAjHJ4rBbfDDuml84S0yll3nzDFCJ/M1nKHz0ZjgNYdc1hI7GRootDo6ZB1vXZtFstxvE5pTxdeKQzrgjTz2CO+8wZgPrHDGIdWEoQ18iFKW/SeXFij022azwgTWvW94u4FRse8D07SKinLeCk2ZwPw7kB3jV8L4iJF1vOudVW1oJl9d6AwhJrEC2Qg== 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, 22 Sep 2025 16:39:53 -0700 Shakeel Butt wrote: > On Mon, Sep 22, 2025 at 04:04:43PM -0700, Andrew Morton wrote: > > On Mon, 22 Sep 2025 15:02:03 -0700 Shakeel Butt wrote: > > > > > Generally memcg charging is allowed from all the contexts including NMI > > > where even spinning on spinlock can cause locking issues. However one > > > call chain was missed during the addition of memcg charging from any > > > context support. That is try_charge_memcg() -> memcg_memory_event() -> > > > cgroup_file_notify(). > > > > > > The possible function call tree under cgroup_file_notify() can acquire > > > many different spin locks in spinning mode. Some of them are > > > cgroup_file_kn_lock, kernfs_notify_lock, pool_workqeue's lock. So, let's > > > just skip cgroup_file_notify() from memcg charging if the context does > > > not allow spinning. > > > > > > Alternative approach was also explored where instead of skipping > > > cgroup_file_notify(), we defer the memcg event processing to irq_work > > > [1]. However it adds complexity and it was decided to keep things simple > > > until we need more memcg events with !allow_spinning requirement. > > > > > > Link: https://lore.kernel.org/all/5qi2llyzf7gklncflo6gxoozljbm4h3tpnuv4u4ej4ztysvi6f@x44v7nz2wdzd/ [1] > > > Signed-off-by: Shakeel Butt > > > Acked-by: Michal Hocko > > > > Fixes a possible kernel deadlock, yes? > > > > Is a cc:stable appropriate and can we identify a Fixes: target? > > > > Thanks. > > > > (Did it ever generate lockdep warnings?) > > The report is here: > https://lore.kernel.org/all/20250905061919.439648-1-yepeilin@google.com/ > > I am not sure about the Fixes tag though or more like which one to put > in the Fixes as we recently started supporting memcg charging for NMI > context or allowing bpf programs to do memcg charged allocations in > recursive context (see the above report for this recursive call chain). > There is no single commit which can be blamed here. I tend to view the Fixes: as us suggesting which kernel versions should be patched. I'm suspecting that's 6.16+, so using the final relevant patch in that release as a Fixes: target would work.