linux-kernel - Re: [PATCH] futex: fix reference leak

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Date:	Mon, 09 Feb 2009 10:53:15 -0800
From:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Darren Hart <dvhltc@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] futex: fix reference leak


Yes. This patch fixes the problem on my system. With git, without the
patch I see the same oops as before on reboot. With the patch, system
reboots cleanly.

A minor typo in the patch
+ ret = -RESTART_RESTARTBLOCK;
should be
+ ret = -ERESTART_RESTARTBLOCK;

Thanks,
Venki

On Mon, 2009-02-09 at 10:26 -0800, Peter Zijlstra wrote:
> Venki, does this perchance solve your issue with my futex patch?
> 
> Darren, could you please have a look at this before Ingo pushes it out
> to Linus?
> 
> ---
> Catalin noticed that (38d47c1b7075: futex: rely on
> get_user_pages() for shared futexes) caused an mm_struct leak.
> 
> Some tracing with the function graph tracer quickly pointed out that
> futex_wait() has exit paths with unbalanced reference counts.
> 
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> ---
>  kernel/futex.c |   23 +++++++++++++++--------
>  1 files changed, 15 insertions(+), 8 deletions(-)
> 
> diff --git a/kernel/futex.c b/kernel/futex.c
> index f89d373..7b76c8e 100644
> --- a/kernel/futex.c
> +++ b/kernel/futex.c
> @@ -1284,18 +1284,23 @@ retry:
>  	 */
>  
>  	/* If we were woken (and unqueued), we succeeded, whatever. */
> -	if (!unqueue_me(&q))
> -		return 0;
> -	if (rem)
> -		return -ETIMEDOUT;
> +	if (!unqueue_me(&q)) {
> +		ret = 0;
> +		goto out_put_key;
> +	}
> +	if (rem) {
> +		ret = -ETIMEDOUT;
> +		goto out_put_key;
> +	}
>  
>  	/*
>  	 * We expect signal_pending(current), but another thread may
>  	 * have handled it for us already.
>  	 */
> -	if (!abs_time)
> -		return -ERESTARTSYS;
> -	else {
> +	if (!abs_time) {
> +		ret = -ERESTARTSYS;
> +		goto out_put_key;
> +	} else {
>  		struct restart_block *restart;
>  		restart = &current_thread_info()->restart_block;
>  		restart->fn = futex_wait_restart;
> @@ -1309,11 +1314,13 @@ retry:
>  			restart->futex.flags |= FLAGS_SHARED;
>  		if (clockrt)
>  			restart->futex.flags |= FLAGS_CLOCKRT;
> -		return -ERESTART_RESTARTBLOCK;
> +		ret = -RESTART_RESTARTBLOCK;
> +		goto out_put_key;
>  	}
>  
>  out_unlock_put_key:
>  	queue_unlock(&q, hb);
> +out_put_key:
>  	put_futex_key(fshared, &q.key);
>  
>  out:
> 
> 

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