From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1njjnu-0022vW-6t for linux-um@lists.infradead.org; Wed, 27 Apr 2022 15:42:14 +0000 Date: Wed, 27 Apr 2022 17:41:59 +0200 From: Oleg Nesterov Subject: Re: [PATCH 9/9] ptrace: Don't change __state Message-ID: <20220427154158.GG17421@redhat.com> References: <878rrrh32q.fsf_-_@email.froward.int.ebiederm.org> <20220426225211.308418-9-ebiederm@xmission.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20220426225211.308418-9-ebiederm@xmission.com> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-um" Errors-To: linux-um-bounces+geert=linux-m68k.org@lists.infradead.org To: "Eric W. Biederman" Cc: linux-kernel@vger.kernel.org, rjw@rjwysocki.net, mingo@kernel.org, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, mgorman@suse.de, bigeasy@linutronix.de, Will Deacon , tj@kernel.org, linux-pm@vger.kernel.org, Peter Zijlstra , Richard Weinberger , Anton Ivanov , Johannes Berg , linux-um@lists.infradead.org, Chris Zankel , Max Filippov , inux-xtensa@linux-xtensa.org, Kees Cook , Jann Horn On 04/26, Eric W. Biederman wrote: > > static void ptrace_unfreeze_traced(struct task_struct *task) > { > - if (READ_ONCE(task->__state) != __TASK_TRACED) > + if (!(READ_ONCE(task->jobctl) & JOBCTL_DELAY_WAKEKILL)) > return; > > WARN_ON(!task->ptrace || task->parent != current); > @@ -213,11 +213,10 @@ static void ptrace_unfreeze_traced(struct task_struct *task) > * Recheck state under the lock to close this race. > */ > spin_lock_irq(&task->sighand->siglock); Now that we do not check __state = __TASK_TRACED, we need lock_task_sighand(). The tracee can be already woken up by ptrace_resume(), but it is possible that it didn't clear DELAY_WAKEKILL yet. Now, before we take ->siglock, the tracee can exit and another thread can do wait() and reap this task. Also, I think the comment above should be updated. I agree, it makes sense to re-check JOBCTL_DELAY_WAKEKILL under siglock just for clarity, but we no longer need to do this to close the race; jobctl &= ~JOBCTL_DELAY_WAKEKILL and wake_up_state() are safe even if JOBCTL_DELAY_WAKEKILL was already cleared. > @@ -2307,6 +2307,7 @@ static int ptrace_stop(int exit_code, int why, int clear_code, > > /* LISTENING can be set only during STOP traps, clear it */ > current->jobctl &= ~JOBCTL_LISTENING; > + current->jobctl &= ~JOBCTL_DELAY_WAKEKILL; minor, but current->jobctl &= ~(JOBCTL_LISTENING | JOBCTL_DELAY_WAKEKILL); looks better. Oleg. _______________________________________________ linux-um mailing list linux-um@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-um