The atomic count value right after reader count increment can be useful to determine the rwsem state at trylock time. So the count value is passed down to rwsem_down_read_slowpath() to be used when appropriate.
Signed-off-by: Waiman Long <[email protected]> --- kernel/locking/rwsem.c | 20 ++++++++++++-------- 1 file changed, 12 insertions(+), 8 deletions(-) diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c index f11b9bd3431d..12761e02ab9b 100644 --- a/kernel/locking/rwsem.c +++ b/kernel/locking/rwsem.c @@ -270,12 +270,12 @@ static inline void rwsem_set_nonspinnable(struct rw_semaphore *sem) owner | RWSEM_NONSPINNABLE)); } -static inline bool rwsem_read_trylock(struct rw_semaphore *sem) +static inline long rwsem_read_trylock(struct rw_semaphore *sem) { long cnt = atomic_long_add_return_acquire(RWSEM_READER_BIAS, &sem->count); if (WARN_ON_ONCE(cnt < 0)) rwsem_set_nonspinnable(sem); - return !(cnt & RWSEM_READ_FAILED_MASK); + return cnt; } /* @@ -989,9 +989,9 @@ rwsem_spin_on_owner(struct rw_semaphore *sem, unsigned long nonspinnable) * Wait for the read lock to be granted */ static struct rw_semaphore __sched * -rwsem_down_read_slowpath(struct rw_semaphore *sem, int state) +rwsem_down_read_slowpath(struct rw_semaphore *sem, int state, long count) { - long count, adjustment = -RWSEM_READER_BIAS; + long adjustment = -RWSEM_READER_BIAS; struct rwsem_waiter waiter; DEFINE_WAKE_Q(wake_q); bool wake = false; @@ -1337,8 +1337,10 @@ static struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem) */ static inline void __down_read(struct rw_semaphore *sem) { - if (!rwsem_read_trylock(sem)) { - rwsem_down_read_slowpath(sem, TASK_UNINTERRUPTIBLE); + long count = rwsem_read_trylock(sem); + + if (count & RWSEM_READ_FAILED_MASK) { + rwsem_down_read_slowpath(sem, TASK_UNINTERRUPTIBLE, count); DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem); } else { rwsem_set_reader_owned(sem); @@ -1347,8 +1349,10 @@ static inline void __down_read(struct rw_semaphore *sem) static inline int __down_read_killable(struct rw_semaphore *sem) { - if (!rwsem_read_trylock(sem)) { - if (IS_ERR(rwsem_down_read_slowpath(sem, TASK_KILLABLE))) + long count = rwsem_read_trylock(sem); + + if (count & RWSEM_READ_FAILED_MASK) { + if (IS_ERR(rwsem_down_read_slowpath(sem, TASK_KILLABLE, count))) return -EINTR; DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem); } else { -- 2.18.1
