From 400db6fe74317d64c920025ed4de2de7b3522230 Mon Sep 17 00:00:00 2001
From: John David Anglin <dave.anglin@bell.net>
Date: Sun, 12 Aug 2018 16:31:17 -0400
Subject: [PATCH] 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>
---
arch/parisc/include/asm/spinlock.h | 8 ++------
1 file changed, 2 insertions(+), 6 deletions(-)
diff --git a/arch/parisc/include/asm/spinlock.h b/arch/parisc/include/asm/spinlock.h
index 64f2992e439f..617efa845054 100644
--- a/arch/parisc/include/asm/spinlock.h
+++ b/arch/parisc/include/asm/spinlock.h
@@ -21,7 +21,6 @@ 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)
@@ -31,16 +30,15 @@ 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)
@@ -48,10 +46,8 @@ 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;
}
--
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