From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1njiNO-001jjn-26 for linux-um@lists.infradead.org; Wed, 27 Apr 2022 14:10:43 +0000 Date: Wed, 27 Apr 2022 16:10:25 +0200 From: Oleg Nesterov Subject: Re: [PATCH 6/9] signal: Always call do_notify_parent_cldstop with siglock held Message-ID: <20220427141018.GA17421@redhat.com> References: <878rrrh32q.fsf_-_@email.froward.int.ebiederm.org> <20220426225211.308418-6-ebiederm@xmission.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20220426225211.308418-6-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: > > @@ -2164,7 +2166,9 @@ static void do_notify_parent_cldstop(struct task_struct *tsk, > } > > sighand = parent->sighand; > - spin_lock_irqsave(&sighand->siglock, flags); > + lock = tsk->sighand != sighand; > + if (lock) > + spin_lock_nested(&sighand->siglock, SINGLE_DEPTH_NESTING); But why is it safe? Suppose we have two tasks, they both trace each other, both call ptrace_stop() at the same time. Of course this is ugly, they both will block. But with this patch in this case we have the trivial ABBA deadlock, no? Oleg. _______________________________________________ linux-um mailing list linux-um@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-um