From mboxrd@z Thu Jan 1 00:00:00 1970 From: ebiederm@xmission.com (Eric W. Biederman) Subject: Re: [PATCH] Introduce ActivePid: in /proc/self/status (v2, was Vpid:) Date: Wed, 15 Jun 2011 12:08:23 -0700 Message-ID: References: <20110615145527.4016.70157.stgit@bahia.local> <20110615184625.GA15573@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: In-Reply-To: <20110615184625.GA15573@redhat.com> (Oleg Nesterov's message of "Wed, 15 Jun 2011 20:46:25 +0200") Sender: linux-kernel-owner@vger.kernel.org To: Oleg Nesterov Cc: Greg Kurz , akpm@linux-foundation.org, containers@lists.osdl.org, linux-kernel@vger.kernel.org, serge@hallyn.com, daniel.lezcano@free.fr, xemul@openvz.org List-Id: containers.vger.kernel.org Oleg Nesterov writes: > On 06/15, Greg Kurz wrote: >> >> @@ -176,6 +177,17 @@ static inline void task_state(struct seq_file *m, struct pid_namespace *ns, >> if (tracer) >> tpid = task_pid_nr_ns(tracer, ns); >> } >> + actpid = 0; >> + sighand = rcu_dereference(p->sighand); >> + if (sighand) { >> + struct pid_namespace *pid_ns; >> + unsigned long flags; >> + spin_lock_irqsave(&sighand->siglock, flags); > > Well. This is not exactly right. We have lock_task_sighand() for this. > > But. Why do you need ->siglock? Why rcu_read_lock() is not enough? > > Hmm. You don't even need pid_ns afaics, you could simply look at > pid->numbers[pid->level]. I got this moving in that direction, but I admit I probably didn't look close enough. I just remember it is always tricky when accessing a process and dealing with races with things like unhash_process(). Eric