linux-kernel - Re: [PATCH] locking/qrwlock: fix write unlock issue in big endian

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Date:	Thu, 02 Jun 2016 12:44:51 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>
Cc:	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	waiman.long@...com, peterz@...radead.org
Subject: Re: [PATCH] locking/qrwlock: fix write unlock issue in big endian

On Thursday, June 2, 2016 6:09:08 PM CEST Pan Xinhui wrote:
> diff --git a/include/asm-generic/qrwlock.h b/include/asm-generic/qrwlock.h
> index 54a8e65..eadd7a3 100644
> --- a/include/asm-generic/qrwlock.h
> +++ b/include/asm-generic/qrwlock.h
> @@ -139,7 +139,7 @@ static inline void queued_read_unlock(struct qrwlock *lock)
>   */
>  static inline void queued_write_unlock(struct qrwlock *lock)
>  {
> -       smp_store_release((u8 *)&lock->cnts, 0);
> +       (void)atomic_sub_return_release(_QW_LOCKED, &lock->cnts);
>  }

Isn't this more expensive than the existing version?

	Arnd
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