linux-kernel - Re: [PATCH UPDATED 06/14] signal: use GROUP_STOP_PENDING to avoid stopping multiple times for a single group stop

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Date:	Sun, 28 Nov 2010 20:07:42 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	roland@...hat.com, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org
Subject: Re: [PATCH UPDATED 06/14] signal: use GROUP_STOP_PENDING to avoid
	stopping multiple times for a single group stop

On 11/27, Tejun Heo wrote:
>
>  static int recalc_sigpending_tsk(struct task_struct *t)
>  {
> -	if (t->signal->group_stop_count > 0 ||
> +	if ((t->group_stop & GROUP_STOP_PENDING) ||

OK, this makes the intent clear.

> @@ -732,6 +732,9 @@ static int prepare_signal(int sig, struct task_struct *p, int from_ancestor_ns)
>  		t = p;
>  		do {
>  			unsigned int state;
> +
> +			t->group_stop = 0;
> +

Yes.

But, afaics, this is not enough. Say, what about zap_other_threads() ?
We shouldn't allow sub-threads to stop in this case.

Basically, every time we clear ->group_stop_count we should also reset
->group_stop for every thread. Fortunately, every time we already do
while_each_thread().

Oleg.

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