ARM: 7632/1: spinlock: avoid exclusive accesses on unlock() path

When unlocking a spinlock, all we need to do is increment the owner
field of the lock. Since only one CPU can be performing an unlock()
operation for a given lock, this doesn't need to be exclusive.

This patch simplifies arch_spin_unlock to use non-exclusive accesses
when updating the owner field of the lock.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

diff --git a/arch/arm/include/asm/spinlock.h b/arch/arm/include/asm/spinlock.h
index b4ca707..6220e9f 100644 (file)
--- a/arch/arm/include/asm/spinlock.h
+++ b/arch/arm/include/asm/spinlock.h
@@ -119,22 +119,8 @@ static inline int arch_spin_trylock(arch_spinlock_t *lock)
 
 static inline void arch_spin_unlock(arch_spinlock_t *lock)
 {
-       unsigned long tmp;
-       u32 slock;
-
        smp_mb();
-
-       __asm__ __volatile__(
-"      mov     %1, #1\n"
-"1:    ldrex   %0, [%2]\n"
-"      uadd16  %0, %0, %1\n"
-"      strex   %1, %0, [%2]\n"
-"      teq     %1, #0\n"
-"      bne     1b"
-       : "=&r" (slock), "=&r" (tmp)
-       : "r" (&lock->slock)
-       : "cc");
-
+       lock->tickets.owner++;
        dsb_sev();
 }