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([2601:188:c180:4250:ecbe:130d:668d:951d]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-4b639dab102sm29277371cf.33.2025.09.12.14.13.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 12 Sep 2025 14:13:11 -0700 (PDT) From: Waiman Long X-Google-Original-From: Waiman Long Message-ID: <6831b9fe-402f-40a6-84e6-b723dd006b90@redhat.com> Date: Fri, 12 Sep 2025 17:13:09 -0400 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] rcu: Remove redundant rcu_read_lock/unlock() in spin_lock critical sections To: pengdonglin , tj@kernel.org, tony.luck@intel.com, jani.nikula@linux.intel.com, ap420073@gmail.com, jv@jvosburgh.net, freude@linux.ibm.com, bcrl@kvack.org, trondmy@kernel.org, kees@kernel.org Cc: bigeasy@linutronix.de, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, linux-nfs@vger.kernel.org, linux-aio@kvack.org, linux-fsdevel@vger.kernel.org, linux-security-module@vger.kernel.org, netdev@vger.kernel.org, intel-gfx@lists.freedesktop.org, linux-acpi@vger.kernel.org, linux-s390@vger.kernel.org, cgroups@vger.kernel.org, pengdonglin , "Paul E . McKenney" References: <20250912065050.460718-1-dolinux.peng@gmail.com> Content-Language: en-US In-Reply-To: <20250912065050.460718-1-dolinux.peng@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 9/12/25 2:50 AM, pengdonglin wrote: > From: pengdonglin > > When CONFIG_PREEMPT_RT is disabled, spin_lock*() operations implicitly > disable preemption, which provides RCU read-side protection. When > CONFIG_PREEMPT_RT is enabled, spin_lock*() implementations internally > manage RCU read-side critical sections. I have some doubt about your claim that disabling preemption provides RCU read-side protection. It is true for some flavors but probably not all. I do know that disabling interrupt will provide RCU read-side protection. So for spin_lock_irq*() calls, that is valid. I am not sure about spin_lock_bh(), maybe it applies there too. we need some RCU people to confirm. When CONFIG_PREEMPT_RT is enabled, rt_spin_lock/unlock() will call rcu_read_lock/_unlock() internally. So eliminating explicit rcu_read_lock/unlock() in critical sections should be fine. Cheers, Longman