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ARM: 7749/1: spinlock: retry trylock operation if strex fails on free lock

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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 <anthony.thompson@arm.com>
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 2013-06-05 11:27:26 +01:00 committed by Russell King
parent 1aa2b3b7a6
commit 15e7e5c1eb
1 changed files with 13 additions and 10 deletions
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23
arch/arm/include/asm/spinlock.h
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@ -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");
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 (tmp == 0) {
if (!contended) {
smp_mb();
return 1;
} else {