From: John David Anglin Date: Sun, 12 Aug 2018 20:31:17 +0000 (-0400) Subject: parisc: Remove unnecessary barriers from spinlock.h X-Git-Tag: v4.14.67~8 X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=6541d98d114ef4ccf923c02ae665262450b3966c;p=users%2Fjedix%2Flinux-maple.git 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 Cc: stable@vger.kernel.org # 4.0+ Signed-off-by: Helge Deller Signed-off-by: Greg Kroah-Hartman --- diff --git a/arch/parisc/include/asm/spinlock.h b/arch/parisc/include/asm/spinlock.h index af03359e6ac5..a82776592c8e 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) @@ -30,16 +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; }