linux-kernel - Re: [PATCH] Introduce ActivePid: in /proc/self/status (v2, was Vpid:)

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Date:	Wed, 15 Jun 2011 12:08:23 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Greg Kurz <gkurz@...ibm.com>, akpm@...ux-foundation.org,
	containers@...ts.osdl.org, linux-kernel@...r.kernel.org,
	serge@...lyn.com, daniel.lezcano@...e.fr, xemul@...nvz.org
Subject: Re: [PATCH] Introduce ActivePid: in /proc/self/status (v2, was Vpid:)

Oleg Nesterov <oleg@...hat.com> 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
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