ARM: spinlock: retry trylock operation if strex fails on free lock
Subsystems (2)
PATCH 1/1 ARM: spinlock: retry trylock operation if strex fails on free lock
An exclusive store instruction may fail for reasons other than lock contention (e.g. a cache eviction during the critical section) so, in line with other architectures using similar exclusive instructions (alpha, mips, powerpc), retry the trylock operation if the lock appears to be free but the strex reported failure.
Reported-by Tony Thompson <[email protected]>
Signed-off-by Will Deacon <[email protected]>
--- arch/arm/include/asm/spinlock.h | 25 ++++++++++++++----------- 1 file changed, 14 insertions(+), 11 deletions(-)
arch/arm/include/asm/spinlock.h +14 -11
@@ -97,19 +97,22 @@ static inline void arch_spin_lock(arch_spinlock_t *lock)static inline int arch_spin_trylock (arch_spinlock_t *lock) { -unsigned long tmp; +unsigned long contended, res;u32 slock; - __asm__ __volatile__( -" ldrex %0, [%2]\n" -" subs %1, %0, %0, ror #16\n" -" addeq %0, %0, %3\n" -" strexeq %1, %0, [%2]" - :"=&r" (slock),"=&r" (tmp) - :"r" (&lock->slock),"I" (1 <<TICKET_SHIFT ) - :"cc" ); - -if (tmp ==0 ) { +do { + __asm__ __volatile__( +" ldrex %0, [%3]\n" +" mov %2, #0\n" +" subs %1, %0, %0, ror #16\n" +" addeq %0, %0, %4\n" +" strexeq %2, %0, [%3]" + :"=&r" (slock),"=&r" (contended),"=r" (res) + :"r" (&lock->slock),"I" (1 <<TICKET_SHIFT ) + :"cc" ); + }while (res); + +if (!contended) {smp_mb ();return 1 ; }else {
Signature · 1 line
1.8.2.2