linux-kernel - Re: [PATCH RFC 21/26] powerpc: Remove spin_unlock

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Date:   Sun, 2 Jul 2017 11:58:07 +0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        parri.andrea@...il.com, dave@...olabs.net,
        manfred@...orfullife.com, arnd@...db.de, peterz@...radead.org,
        netdev@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        will.deacon@....com, oleg@...hat.com, mingo@...hat.com,
        netfilter-devel@...r.kernel.org, tj@...nel.org,
        stern@...land.harvard.edu, akpm@...ux-foundation.org,
        torvalds@...ux-foundation.org, Paul Mackerras <paulus@...ba.org>
Subject: Re: [PATCH RFC 21/26] powerpc: Remove spin_unlock_wait()
 arch-specific definitions

On Thu, Jun 29, 2017 at 05:01:29PM -0700, Paul E. McKenney wrote:
> There is no agreed-upon definition of spin_unlock_wait()'s semantics,
> and it appears that all callers could do just as well with a lock/unlock
> pair.  This commit therefore removes the underlying arch-specific
> arch_spin_unlock_wait().
> 
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: <linuxppc-dev@...ts.ozlabs.org>
> Cc: Will Deacon <will.deacon@....com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Alan Stern <stern@...land.harvard.edu>
> Cc: Andrea Parri <parri.andrea@...il.com>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>

Acked-by: Boqun Feng <boqun.feng@...il.com>

Regards,
Boqun

> ---
>  arch/powerpc/include/asm/spinlock.h | 33 ---------------------------------
>  1 file changed, 33 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/spinlock.h b/arch/powerpc/include/asm/spinlock.h
> index 8c1b913de6d7..d256e448ea49 100644
> --- a/arch/powerpc/include/asm/spinlock.h
> +++ b/arch/powerpc/include/asm/spinlock.h
> @@ -170,39 +170,6 @@ static inline void arch_spin_unlock(arch_spinlock_t *lock)
>  	lock->slock = 0;
>  }
>  
> -static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
> -{
> -	arch_spinlock_t lock_val;
> -
> -	smp_mb();
> -
> -	/*
> -	 * Atomically load and store back the lock value (unchanged). This
> -	 * ensures that our observation of the lock value is ordered with
> -	 * respect to other lock operations.
> -	 */
> -	__asm__ __volatile__(
> -"1:	" PPC_LWARX(%0, 0, %2, 0) "\n"
> -"	stwcx. %0, 0, %2\n"
> -"	bne- 1b\n"
> -	: "=&r" (lock_val), "+m" (*lock)
> -	: "r" (lock)
> -	: "cr0", "xer");
> -
> -	if (arch_spin_value_unlocked(lock_val))
> -		goto out;
> -
> -	while (lock->slock) {
> -		HMT_low();
> -		if (SHARED_PROCESSOR)
> -			__spin_yield(lock);
> -	}
> -	HMT_medium();
> -
> -out:
> -	smp_mb();
> -}
> -
>  /*
>   * Read-write spinlocks, allowing multiple readers
>   * but only one writer.
> -- 
> 2.5.2
> 

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