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

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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>
This commit is contained in:
Will Deacon 2013-01-24 14:47:38 +01:00 committed by Russell King
parent 0a301110b7
commit 20e260b6f4
1 changed files with 1 additions and 15 deletions
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16
arch/arm/include/asm/spinlock.h
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@ -119,22 +119,8 @@ static inline int arch_spin_trylock(arch_spinlock_t *lock)
static inline void arch_spin_unlock(arch_spinlock_t *lock) static inline void arch_spin_unlock(arch_spinlock_t *lock)
{ {
unsigned long tmp;
u32 slock;
smp_mb(); smp_mb();
lock->tickets.owner++;
__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");
dsb_sev(); dsb_sev();
} }