linux-kernel - Re: [PATCH] futex: Prevent pi_state from double freeing in case of error

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Date:	Fri, 18 Dec 2015 15:08:03 -0800
From:	Darren Hart <dvhart@...radead.org>
To:	Bhuvanesh_Surachari@...tor.com
Cc:	tglx@...utronix.de, peterz@...radead.org, mingo@...nel.org,
	dave@...olabs.net, akpm@...ux-foundation.org,
	linux@...musvillemoes.dk, viresh.kumar@...aro.org,
	luto@...capital.net, bigeasy@...utronix.de, mtk.manpages@...il.com,
	linux-kernel@...r.kernel.org, Andy Lowe <Andy_Lowe@...tor.com>
Subject: Re: [PATCH] futex: Prevent pi_state from double freeing in case of
 error

On Fri, Dec 18, 2015 at 02:13:43PM +0530, Bhuvanesh_Surachari@...tor.com wrote:
> From: Bhuvanesh Surachari <bhuvanesh_surachari@...tor.com>
> 
> In case of error from rt_mutex_start_proxy_lock pi_state is freed
> twice in futex_requeue function. Hence removing free_pi_state in
> else branch and branching to the location where pi_state is freed.
> 
> Signed-off-by: Bhuvanesh Surachari <Bhuvanesh_Surachari@...tor.com>
> Signed-off-by: Andy Lowe <Andy_Lowe@...tor.com>

Apparently inadvertently introduced by:

commit 30a6b8031fe14031ab27c1fa3483cb9780e7f63c
    futex: Fix a race condition between REQUEUE_PI and task death

Reviewed-by: Darren Hart <dvhart@...ux.intel.com>

> ---
>  kernel/futex.c |    1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/kernel/futex.c b/kernel/futex.c
> index 684d754..264b3f2 100644
> --- a/kernel/futex.c
> +++ b/kernel/futex.c
> @@ -1815,7 +1815,6 @@ retry_private:
>  			} else if (ret) {
>  				/* -EDEADLK */
>  				this->pi_state = NULL;
> -				free_pi_state(pi_state);
>  				goto out_unlock;
>  			}
>  		}
> -- 
> 1.7.9.5
> 
> 
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-- 
Darren Hart
Intel Open Source Technology Center
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