linux-kernel - Re: [PATCH] ARCv2: spinlock: remove the extra smp

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Message-ID: <20190308083748.GP32477@hirez.programming.kicks-ass.net>
Date:   Fri, 8 Mar 2019 09:37:48 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vineet Gupta <vineet.gupta1@...opsys.com>
Cc:     linux-snps-arc@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARCv2: spinlock: remove the extra smp_mb before lock,
 after unlock

On Thu, Mar 07, 2019 at 05:35:46PM -0800, Vineet Gupta wrote:
> @@ -68,8 +72,6 @@ static inline void arch_spin_unlock(arch_spinlock_t *lock)
>  	smp_mb();
>  
>  	lock->slock = __ARCH_SPIN_LOCK_UNLOCKED__;
> -
> -	smp_mb();
>  }
>  
>  /*

> @@ -226,8 +218,6 @@ static inline void arch_write_unlock(arch_rwlock_t *rw)
>  	smp_mb();
>  
>  	rw->counter = __ARCH_RW_LOCK_UNLOCKED__;
> -
> -	smp_mb();
>  }
>  
>  #else	/* !CONFIG_ARC_HAS_LLSC */

I'm thinking those assignments should be WRITE_ONCE() at the very least.