parisc: Remove unnecessary barriers from spinlock.h

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>

diff --git a/arch/parisc/include/asm/spinlock.h b/arch/parisc/include/asm/spinlock.h
index af03359e6ac5685d6fa93361b5a0f4f4817a8cae..a82776592c8e5e8a346dadb8f753e18082bcccaf 100644 (file)
--- a/arch/parisc/include/asm/spinlock.h
+++ b/arch/parisc/include/asm/spinlock.h
@@ -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;
 }