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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48c622704a5sm12255235f8f.15.2026.10.05.11.46.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 05 Oct 2026 11:46:56 -0700 (PDT) Date: Mon, 5 Oct 2026 19:46:55 +0100 From: David Laight To: Oleg Nesterov Cc: Babanpreet Singh , Christian Brauner , Pavel Tikhomirov , Andrew Morton , linux-kernel@vger.kernel.org, syzbot+c382ee653fd70f5cf1bb@syzkaller.appspotmail.com Subject: Re: [PATCH] pid: use READ_ONCE() in pid_alive() Message-ID: <20261005194655.18e8d3a2@pumpkin> In-Reply-To: References: <20261002012141.7-1-bbnpreetsingh@gmail.com> <20261003182224.2171b574@pumpkin> <20261004125118.7de53b47@pumpkin> <20261004143108.4b851713@pumpkin> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Mon, 5 Oct 2026 17:03:42 +0200 Oleg Nesterov wrote: > On 10/04, David Laight wrote: ... > > If the 'add code' all the readers and have to hold the lock then does that > > leave anything other than task exit doing an rcu-delete. > > I wouldn't have though acquiring the lock in the task exit code would > > be noticeable. > > Still can't understand. The exiting task does take tasklist when it calls > detach_pid(). I think I've confused myself :-) The delete needs the lock to avoid corrupting the list. It would be safe for an rcu protected reader - but it doesn't help you. David