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[195.250.132.146]) by smtp.gmail.com with UTF8SMTPSA id 5b1f17b1804b1-45b8f2d3c88sm300994075e9.19.2025.09.08.02.08.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 08 Sep 2025 02:08:23 -0700 (PDT) Date: Mon, 8 Sep 2025 11:08:22 +0200 From: Michal Hocko To: Peilin Ye Cc: Shakeel Butt , Andrew Morton , Tejun Heo , Johannes Weiner , Roman Gushchin , Muchun Song , Alexei Starovoitov , Kumar Kartikeya Dwivedi , bpf@vger.kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Meta kernel team Subject: Re: [PATCH] memcg: skip cgroup_file_notify if spinning is not allowed Message-ID: References: <20250905201606.66198-1-shakeel.butt@linux.dev> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Fri 05-09-25 20:48:46, Peilin Ye wrote: > On Fri, Sep 05, 2025 at 01:16:06PM -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. > > > > Signed-off-by: Shakeel Butt > > Tested-by: Peilin Ye > > The repro described in [1] no longer triggers locking issues after > applying this patch and making __bpf_async_init() use __GFP_HIGH > instead of GFP_ATOMIC: > > --- a/kernel/bpf/helpers.c > +++ b/kernel/bpf/helpers.c > @@ -1275,7 +1275,7 @@ static int __bpf_async_init(struct bpf_async_kern *async, struct bpf_map *map, u > } > > /* allocate hrtimer via map_kmalloc to use memcg accounting */ > - cb = bpf_map_kmalloc_node(map, size, GFP_ATOMIC, map->numa_node); > + cb = bpf_map_kmalloc_node(map, size, __GFP_HIGH, map->numa_node); Why do you need to consume memory reserves? Shouldn't kmalloc_nolock be used instead here? > if (!cb) { > ret = -ENOMEM; > goto out; > > [1] https://lore.kernel.org/bpf/20250905061919.439648-1-yepeilin@google.com/#t > > Thanks, > Peilin Ye -- Michal Hocko SUSE Labs