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Wed, 11 Feb 2026 02:53:49 -0800 (PST) Received: from milan ([2001:9b1:d5a0:a500::24b]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-59e5f5a50a1sm267273e87.57.2026.02.11.02.53.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 11 Feb 2026 02:53:48 -0800 (PST) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Wed, 11 Feb 2026 11:53:46 +0100 To: Harry Yoo Cc: Uladzislau Rezki , Andrew Morton , Vlastimil Babka , Christoph Lameter , David Rientjes , Roman Gushchin , Johannes Weiner , Shakeel Butt , Michal Hocko , Hao Li , Alexei Starovoitov , Puranjay Mohan , Andrii Nakryiko , Amery Hung , Catalin Marinas , "Paul E . McKenney" , Frederic Weisbecker , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Dave Chinner , Qi Zheng , Muchun Song , rcu@vger.kernel.org, linux-mm@kvack.org, bpf@vger.kernel.org Subject: Re: [RFC PATCH 1/7] mm/slab: introduce k[v]free_rcu() with struct rcu_ptr Message-ID: References: <20260206093410.160622-1-harry.yoo@oracle.com> <20260206093410.160622-2-harry.yoo@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: D7648A000B X-Stat-Signature: fjtyxwmi4z58qrcy7k77zbhhoa4jkse8 X-Rspam-User: X-HE-Tag: 1770807231-865300 X-HE-Meta: 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 JgXH+HQQ 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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: On Wed, Feb 11, 2026 at 07:44:37PM +0900, Harry Yoo wrote: > On Wed, Feb 11, 2026 at 11:16:51AM +0100, Uladzislau Rezki wrote: > > If this is supposed to be invoked from NMI, should we better just detect > > such context in the kvfree_call_rcu()? There are lot of "allow_spin" checks > > which make it easy to get lost. > > Detecting if it's NMI might be okay, but IIUC re-entrancy requirement > not only comes from NMI but also from attaching bpf programs to > kernel functions, something like: > > "Run a BPF program whenever queue_delayed_work() is called, > ... and the BPF program somehow frees memory via kfree_rcu_nolock()". > > Then, by the time the kernel calls queue_delayed_work() while holding > krcp->lock, it run the BPF program and calls kfree_rcu_nolock(), > it is not allowed to spin on krcp->lock. > > > > As i see you maintain llist and the idea is simply to re-enter to the > > kvfree_rcu() again with allow-spin=true, since then it will be "normal" > > context. > > It tries to acquire the lock and add it to krcp->head, but if somebody > is already holding the lock, it re-runs kvfree_rcu() with irq work. > Check no_spin on entry, if true, llist_add, queue-irq-work. Re-enter. You might need to set-up interval to prevent frequent bouncing. -- Uladzislau Rezki