linux-kernel - Re: [PATCH 03/16] signal: remove superflous try_to_freeze() loop in do_signal

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Message-ID: <20101220145937.GB11583@redhat.com>
Date:	Mon, 20 Dec 2010 15:59:38 +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,
	rjw@...k.pl, jan.kratochvil@...hat.com
Subject: Re: [PATCH 03/16] signal: remove superflous try_to_freeze() loop
	in do_signal_stop()

On 12/06, Tejun Heo wrote:
>
> do_signal_stop() is used only by get_signal_to_deliver() and after a
> successful signal stop, it always calls try_to_freeze(), so the
> try_to_freeze() loop around schedule() in do_signal_stop() is
> superflous and confusing.  Remove it.

I think the patch is obvioulsy fine.

Acked-by: Oleg Nesterov <oleg@...hat.com>



But I am a bit confused, a couple of off-topic questions to Rafael.

> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -1781,9 +1781,7 @@ static int do_signal_stop(int signr)
>  	}
>
>  	/* Now we don't run again until woken by SIGCONT or SIGKILL */
> -	do {
> -		schedule();
> -	} while (try_to_freeze());
> +	schedule();

I am wondering what was the purpose of this do/while loop. Probably
this was just oversight. We always return in TASK_RUNNING state from
schedule, try_to_freeze() should return the task in this state too.

My question is: refrigerator() tries to preserve the caller's state.
Why? I think it is just wrong to call refrigerator() unless the
task is TASK_RUNNING, no? If no, then the games with saving/restoring
->state look obviously racy/wrong.

Oleg.

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