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

From: Darren Hart
Date: Fri Dec 18 2015 - 18:08:15 EST


On Fri, Dec 18, 2015 at 02:13:43PM +0530, Bhuvanesh_Surachari@xxxxxxxxxx wrote:
> From: Bhuvanesh Surachari <bhuvanesh_surachari@xxxxxxxxxx>
>
> 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@xxxxxxxxxx>
> Signed-off-by: Andy Lowe <Andy_Lowe@xxxxxxxxxx>

Apparently inadvertently introduced by:

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

Reviewed-by: Darren Hart <dvhart@xxxxxxxxxxxxxxx>

> ---
> 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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