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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a18be96549sm399676705e9.6.2026.10.12.05.54.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 12 Oct 2026 05:54:55 -0700 (PDT) Date: Mon, 12 Oct 2026 13:54:54 +0100 From: David Laight To: Oleg Nesterov Cc: Andrew Morton , Christian Brauner , Mingyu Wang <25181214217@stu.xidian.edu.cn>, linux-kernel@vger.kernel.org Subject: Re: [PATCH] pid: document that do_each_pid_task() needs tasklist_lock Message-ID: <20261012135454.4eda3fa8@pumpkin> In-Reply-To: References: 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 Sun, 11 Oct 2026 16:16:51 +0200 Oleg Nesterov wrote: > do_each_pid_task() looks "obviously rcu-safe". This confuses people > and we already have 2 buggy users: send_sigio() and send_sigurg(). > > The reasons why it is not are not obvious at all, add the comment. > > Signed-off-by: Oleg Nesterov > --- > include/linux/pid.h | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/include/linux/pid.h b/include/linux/pid.h > index ddaef0bbc8ba..f5476d7140a3 100644 > --- a/include/linux/pid.h > +++ b/include/linux/pid.h > @@ -187,6 +187,15 @@ static inline pid_t pid_nr(struct pid *pid) > pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns); > pid_t pid_vnr(struct pid *pid); > > +/* > + * Needs tasklist_lock if type > PIDTYPE_TGID. A lockless reader can: Think I'd be more explicit, so: ... if type isn't PIDTYPE_PID or PIDTYPE_TGID. David > + * > + * - race with a change_pid() that moves the task to another hlist, > + * and continue to scan the wrong list. > + * > + * - race with a copy_process() that adds a new task to the start of hlist, > + * and miss the new child. > + */ > #define do_each_pid_task(pid, type, task) \ > do { \ > if ((pid) != NULL) \