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Commit 6541d98d authored by John David Anglin's avatar John David Anglin Committed by Greg Kroah-Hartman
Browse files

parisc: Remove unnecessary barriers from spinlock.h 



commit 3b885ac1 upstream.

Now that mb() is an instruction barrier, it will slow performance if we issue
unnecessary barriers.

The spinlock defines have a number of unnecessary barriers.  The __ldcw()
define is both a hardware and compiler barrier.  The mb() barriers in the
routines using __ldcw() serve no purpose.

The only barrier needed is the one in arch_spin_unlock().  We need to ensure
all accesses are complete prior to releasing the lock.

Signed-off-by: default avatarJohn David Anglin <dave.anglin@bell.net>
Cc: stable@vger.kernel.org # 4.0+
Signed-off-by: default avatarHelge Deller <deller@gmx.de>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 3f59cf41

arch/parisc/include/asm/spinlock.h

+2 −6
Original line number Diff line number Diff line
@@ -20,7 +20,6 @@ static inline void arch_spin_lock_flags(arch_spinlock_t *x, 
{

	volatile unsigned int *a;



	mb();

	a = __ldcw_align(x);

	while (__ldcw(a) == 0)

		while (*a == 0)
@@ -30,16 +29,15 @@ static inline void arch_spin_lock_flags(arch_spinlock_t *x, 
				local_irq_disable();

			} else

				cpu_relax();

	mb();

}



static inline void arch_spin_unlock(arch_spinlock_t *x)

{

	volatile unsigned int *a;

	mb();



	a = __ldcw_align(x);

	*a = 1;

	mb();

	*a = 1;

}



static inline int arch_spin_trylock(arch_spinlock_t *x)
@@ -47,10 +45,8 @@ static inline int arch_spin_trylock(arch_spinlock_t *x) 
	volatile unsigned int *a;

	int ret;



	mb();

	a = __ldcw_align(x);

        ret = __ldcw(a) != 0;

	mb();



	return ret;

}