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ARM: 7812/1: rwlocks: retry trylock operation if strex fails on free lock 

Commit 15e7e5c1eb ("ARM: 7749/1: spinlock: retry trylock operation if
strex fails on free lock") modifying our arch_spin_trylock to retry the
acquisition if the lock appeared uncontended, but the strex failed.

This patch does the same for rwlocks, which were missed by the original
patch.

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 2013-08-12 18:04:05 +01:00 committed by Russell King
parent afa31d8eb8
commit 00efaa0250
1 changed files with 30 additions and 19 deletions
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49
arch/arm/include/asm/spinlock.h
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@ -168,17 +168,20 @@ static inline void arch_write_lock(arch_rwlock_t *rw)
static inline int arch_write_trylock(arch_rwlock_t *rw)
{
unsigned long tmp;
unsigned long contended, res;
__asm__ __volatile__(
" ldrex %0, [%1]\n"
" teq %0, #0\n"
" strexeq %0, %2, [%1]"
: "=&r" (tmp)
: "r" (&rw->lock), "r" (0x80000000)
: "cc");
do {
__asm__ __volatile__(
" ldrex %0, [%2]\n"
" mov %1, #0\n"
" teq %0, #0\n"
" strexeq %1, %3, [%2]"
: "=&r" (contended), "=&r" (res)
: "r" (&rw->lock), "r" (0x80000000)
: "cc");
} while (res);
if (tmp == 0) {
if (!contended) {
smp_mb();
return 1;
} else {
@ -254,18 +257,26 @@ static inline void arch_read_unlock(arch_rwlock_t *rw)
static inline int arch_read_trylock(arch_rwlock_t *rw)
{
unsigned long tmp, tmp2 = 1;
unsigned long contended, res;
__asm__ __volatile__(
" ldrex %0, [%2]\n"
" adds %0, %0, #1\n"
" strexpl %1, %0, [%2]\n"
: "=&r" (tmp), "+r" (tmp2)
: "r" (&rw->lock)
: "cc");
do {
__asm__ __volatile__(
" ldrex %0, [%2]\n"
" mov %1, #0\n"
" adds %0, %0, #1\n"
" strexpl %1, %0, [%2]"
: "=&r" (contended), "=&r" (res)
: "r" (&rw->lock)
: "cc");
} while (res);
smp_mb();
return tmp2 == 0;
/* If the lock is negative, then it is already held for write. */
if (contended < 0x80000000) {
smp_mb();
return 1;
} else {
return 0;
}
}
/* read_can_lock - would read_trylock() succeed? */