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[146.241.10.172]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-395cb318acfsm15911566f8f.70.2025.03.17.10.29.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 17 Mar 2025 10:29:53 -0700 (PDT) Message-ID: <99214ac9-cff7-4a5c-b439-ed9ec2c6877c@redhat.com> Date: Mon, 17 Mar 2025 18:29:51 +0100 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net-next 06/18] netfilter: nf_dup{4, 6}: Move duplication check to task_struct. To: Sebastian Andrzej Siewior , Peter Zijlstra , Juri Lelli , Valentin Schneider Cc: "David S. Miller" , Eric Dumazet , Jakub Kicinski , Simon Horman , Thomas Gleixner , Pablo Neira Ayuso , Jozsef Kadlecsik , Ingo Molnar , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , netdev@vger.kernel.org, linux-rt-devel@lists.linux.dev References: <20250309144653.825351-1-bigeasy@linutronix.de> <20250309144653.825351-7-bigeasy@linutronix.de> Content-Language: en-US From: Paolo Abeni In-Reply-To: <20250309144653.825351-7-bigeasy@linutronix.de> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Hi, On 3/9/25 3:46 PM, Sebastian Andrzej Siewior wrote: > nf_skb_duplicated is a per-CPU variable and relies on disabled BH for its > locking. Without per-CPU locking in local_bh_disable() on PREEMPT_RT > this data structure requires explicit locking. > > Due to the recursion involved, the simplest change is to make it a > per-task variable. > > Move the per-CPU variable nf_skb_duplicated to task_struct and name it > in_nf_duplicate. Add it to the existing bitfield so it doesn't use > additional memory. > > Cc: Pablo Neira Ayuso > Cc: Jozsef Kadlecsik > Cc: Ingo Molnar > Cc: Peter Zijlstra > Cc: Juri Lelli > Cc: Vincent Guittot > Cc: Dietmar Eggemann > Cc: Steven Rostedt > Cc: Ben Segall > Cc: Mel Gorman > Cc: Valentin Schneider > Signed-off-by: Sebastian Andrzej Siewior I'm not a super-fan of adding more flags to 'struct task', but in this specific case I agree is the better option, as otherwise we should acquire the local lock for a relatively large scope - the whole packet processing by nft, right? Still this needs some explicit ack from the relevant maintainers. @Peter, @Juri, @Valentin: could you please have a look? Thanks! Paolo