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parisc: Remove unnecessary barriers from spinlock.h

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commit 3b885ac1dc35b87a39ee176a6c7e2af9c789d8b8 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: John David Anglin <dave.anglin@bell.net>
Cc: stable@vger.kernel.org # 4.0+
Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
John David Anglin 2018-08-12 16:31:17 -04:00 committed by Greg Kroah-Hartman
parent 3f59cf41fb
commit 6541d98d11
1 changed files with 2 additions and 6 deletions
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8
arch/parisc/include/asm/spinlock.h
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@ -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;
}