linux-kernel - Re: [PATCH] posix-cpu-timers: fix nanosleep task

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Message-ID: <20130206161011.GA11161@redhat.com>
Date:	Wed, 6 Feb 2013 17:10:11 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Stanislaw Gruszka <sgruszka@...hat.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Dave Jones <davej@...hat.com>,
	John Stultz <john.stultz@...aro.org>,
	Tommi Rantala <tt.rantala@...il.com>
Subject: Re: [PATCH] posix-cpu-timers: fix nanosleep task_struct leak

Stanislaw,

First of all, thank you so much. I knew it was a good idea to cc you ;)

And let me repeat that I forgot everything about this code.

On 02/06, Stanislaw Gruszka wrote:
>
> In do_cpu_nanosleep() we do posix_cpu_timer_create(), but forgot
> corresponding posix_cpu_timer_del(), what lead to task_struct leak.

Plus, it seems we can leave the timer on ->cpu_timers list...

> @@ -1403,6 +1403,7 @@ static int do_cpu_nanosleep(const clockid_t which_clock, int flags,
>  				/*
>  				 * Our timer fired and was reset.
>  				 */
> +				posix_cpu_timer_del(&timer);
>  				spin_unlock_irq(&timer.it_lock);
>  				return 0;
>  			}
> @@ -1420,9 +1421,17 @@ static int do_cpu_nanosleep(const clockid_t which_clock, int flags,
>  		 * We were interrupted by a signal.
>  		 */
>  		sample_to_timespec(which_clock, timer.it.cpu.expires, rqtp);
> -		posix_cpu_timer_set(&timer, 0, &zero_it, it);
> +		error = posix_cpu_timer_set(&timer, 0, &zero_it, it);
> +		if (!error)
> +			posix_cpu_timer_del(&timer);
>  		spin_unlock_irq(&timer.it_lock);
>
> +		while (error == TIMER_RETRY) {
> +			spin_lock_irq(&timer.it_lock);
> +			error = posix_cpu_timer_del(&timer);

It is not clear to me why other posix_cpu_timer_del's above can't fail..
May be you can add a comment.

And I am not sure that TIMER_RETRY is the only error we should worry.
And perhaps we need even more posix_cpu_timer_del's?

For example. Suppose that posix_cpu_timer_create() succeeds and does
get_task_struct(p). But than p dies, and the first posix_cpu_timer_set()
fails with -ESRCH. No?

Oleg.

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