Even with waiting writers, if the lock can be grabbed by a new writer, simply grab it.
Derived from Michel Lespinasse's write lock stealing work on rwsem. Cc: Michel Lespinasse <[email protected]> Signed-off-by: Peter Hurley <[email protected]> --- drivers/tty/tty_ldsem.c | 18 +++++++++++------- 1 file changed, 11 insertions(+), 7 deletions(-) diff --git a/drivers/tty/tty_ldsem.c b/drivers/tty/tty_ldsem.c index 372e897..fd95950 100644 --- a/drivers/tty/tty_ldsem.c +++ b/drivers/tty/tty_ldsem.c @@ -325,7 +325,7 @@ static inline int __ldsem_down_write_nested(struct ld_semaphore *sem, count = atomic_long_add_return(LDSEM_WRITE_BIAS, (atomic_long_t *)&sem->count); - if (count != LDSEM_WRITE_BIAS) { + if ((count & LDSEM_ACTIVE_MASK) != LDSEM_ACTIVE_BIAS) { lock_stat(sem, contended); if (!down_write_failed(sem, timeout)) { lockdep_release(sem, 1, _RET_IP_); @@ -380,12 +380,16 @@ int ldsem_down_write_trylock(struct ld_semaphore *sem) { long count; - count = atomic_long_cmpxchg(&sem->count, LDSEM_UNLOCKED, - LDSEM_WRITE_BIAS); - if (count == LDSEM_UNLOCKED) { - lockdep_acquire(sem, 0, 1, _RET_IP_); - lock_stat(sem, acquired); - return 1; + while (((count = sem->count) & LDSEM_ACTIVE_MASK) == 0) { + long tmp; + + tmp = atomic_long_cmpxchg(&sem->count, count, + count + LDSEM_WRITE_BIAS); + if (count == tmp) { + lockdep_acquire(sem, 0, 1, _RET_IP_); + lock_stat(sem, acquired); + return 1; + } } return 0; } -- 1.8.1.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
