The patch below does not apply to the 4.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 3b885ac1dc35b87a39ee176a6c7e2af9c789d8b8 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 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit
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
diff --git a/arch/parisc/include/asm/spinlock.h b/arch/parisc/include/asm/spinlock.h index 6f84b6acc86e..8a63515f03bf 100644 --- 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) @@ -30,17 +29,16 @@ static inline void arch_spin_lock_flags(arch_spinlock_t *x, local_irq_disable(); } else cpu_relax(); - mb(); } #define arch_spin_lock_flags arch_spin_lock_flags
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; }