Re: [PATCH v8 4/4] qrwlock: Use smp_store_release() in write_unlock()

[Daniel J Blueman]

On Thursday, 9 January 2014 01:10:03 UTC+8, Waiman Long  wrote:
> This patch modifies the queue_write_unlock() function to use the
> new smp_store_release() function in another pending patch. It also
> removes the temporary implementation of smp_load_acquire() and
> smp_store_release() function in qrwlock.c.
>
> This patch should only be merged if PeterZ's linux-arch patch patch
> was merged.
>
> Signed-off-by: Waiman Long <Waiman.Long@xxxxxx>
> Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> ---
>  include/asm-generic/qrwlock.h |    4 +---
>  kernel/locking/qrwlock.c      |   34 ----------------------------------
>  2 files changed, 1 insertions(+), 37 deletions(-)
>
> diff --git a/include/asm-generic/qrwlock.h 
b/include/asm-generic/qrwlock.h
> index 2b9a7b4..4d4bd04 100644
> --- a/include/asm-generic/qrwlock.h
> +++ b/include/asm-generic/qrwlock.h
> @@ -179,9 +179,7 @@ static inline void queue_write_unlock(struct 
qrwlock *lock)
>  	/*
>  	 * Make sure that none of the critical section will be leaked out.
>  	 */
> -	smp_mb__before_clear_bit();
> -	ACCESS_ONCE(lock->cnts.writer) = 0;
> -	smp_mb__after_clear_bit();
> +	smp_store_release(&lock->cnts.writer, 0)

This will fail compilation, so probably needs further testing with 
Peter's load_acquire/store_release barrier patches.

Thanks,
  Daniel
--
Daniel J Blueman
Principal Software Engineer, Numascale
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