linux-kernel - Re: [PATCH v8 4/4] qrwlock: Use smp_store_release() in write

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Date:	Mon, 13 Jan 2014 10:47:36 +0800
From:	Daniel J Blueman <daniel@...ascale.com>
To:	Waiman Long <Waiman.Long@...com>
CC:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v8 4/4] qrwlock: Use smp_store_release() in write_unlock()

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@...com>
 > Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
 > ---
 >  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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