linux-kernel - Re: [PATCH] futex: remove the pointer math from double_unlock

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Message-ID: <alpine.LFD.2.00.0903131022440.29264@localhost.localdomain>
Date:	Fri, 13 Mar 2009 10:26:07 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Darren Hart <dvhltc@...ibm.com>
cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH] futex: remove the pointer math from double_unlock_hb

On Thu, 12 Mar 2009, Darren Hart wrote:
> I mistakenly included the pointer value ordering in the double_unlock_hb
> in my previous patch.  It's only necessary in the double_lock_hb
> function.  This patch removes it.
> 
> Signed-off-by: Darren Hart <dvhltc@...ibm.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: Rusty Russell <rusty@...tcorp.com.au>
> ---
> 
>  kernel/futex.c |   10 ++--------
>  1 files changed, 2 insertions(+), 8 deletions(-)
> 
> diff --git a/kernel/futex.c b/kernel/futex.c
> index 9c97f67..2331b73 100644
> --- a/kernel/futex.c
> +++ b/kernel/futex.c
> @@ -658,14 +658,8 @@ double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
>  static inline void
>  double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
>  {
> -	if (hb1 <= hb2) {
> -		spin_unlock(&hb2->lock);
> -		if (hb1 < hb2)
> -			spin_unlock(&hb1->lock);
> -	} else { /* hb1 > hb2 */
> -		spin_unlock(&hb1->lock);
> -		spin_unlock(&hb2->lock);
> -	}
> +	spin_unlock(&hb1->lock);
> +	spin_unlock(&hb2->lock);

This is missing the check for hb1 == hb2. As I said before:

> Can we just put the code into double_unlock_hb() which gets replaced ?
>
> i.e:
>
>        spin_unlock(&hb1->lock);
>        if (hb1 != hb2)
>              spin_unlock(&hb2->lock);

Thanks,

	tglx
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