linux-kernel - Re: [tip:core/futexes] futex: remove the pointer math from double_unlock

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Date:	Fri, 13 Mar 2009 08:03:43 -0700
From:	Darren Hart <dvhltc@...ibm.com>
To:	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, mingo@...e.hu
CC:	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:core/futexes] futex: remove the pointer math from double_unlock_hb,
 fix

Ingo Molnar wrote:
> Commit-ID:  88f502fedba82eff252b6420e8b8328e4ae25c67
> Gitweb:     http://git.kernel.org/tip/88f502fedba82eff252b6420e8b8328e4ae25c67
> Author:     Ingo Molnar <mingo@...e.hu>
> AuthorDate: Fri, 13 Mar 2009 10:32:07 +0100
> Commit:     Ingo Molnar <mingo@...e.hu>
> CommitDate: Fri, 13 Mar 2009 10:32:07 +0100
> 
> futex: remove the pointer math from double_unlock_hb, fix
> 
> Impact: fix double unlock crash
> 
> Thomas Gleixner noticed that the simplified double_unlock_hb()
> became ... too unsophisticated: in the hb1 == hb2 case it will
> do a double unlock.

Gah.  Thanks for catching it.

> 
> Reported-by: Thomas Gleixner <tglx@...utronix.de>
> Cc: Darren Hart <dvhltc@...ibm.com>
> LKML-Reference: <20090312221118.11146.68610.stgit@...n>
> Signed-off-by: Ingo Molnar <mingo@...e.hu>

Acked-by: Darren Hart <dvhltc@...ibm.com>

> 
> 
> ---
>  kernel/futex.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/futex.c b/kernel/futex.c
> index 2331b73..6b50a02 100644
> --- a/kernel/futex.c
> +++ b/kernel/futex.c
> @@ -659,7 +659,8 @@ static inline void
>  double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
>  {
>  	spin_unlock(&hb1->lock);
> -	spin_unlock(&hb2->lock);
> +	if (hb1 != hb2)
> +		spin_unlock(&hb2->lock);
>  }
> 
>  /*


-- 
Darren Hart
IBM Linux Technology Center
Real-Time Linux Team
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