From c8fe8b0564388f41147326f31e4587171aacccd4 Mon Sep 17 00:00:00 2001 From: Waiman Long Date: Fri, 20 Nov 2020 23:14:12 -0500 Subject: [PATCH] locking/rwsem: Pass the current atomic count to rwsem_down_read_slowpath() 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 Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Davidlohr Bueso Link: https://lkml.kernel.org/r/20201121041416.12285-2-longman@redhat.com --- kernel/locking/rwsem.c | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-) diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c index 67ae366d08dda..5768b90223c06 100644 --- a/kernel/locking/rwsem.c +++ b/kernel/locking/rwsem.c @@ -270,14 +270,14 @@ 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 bool rwsem_read_trylock(struct rw_semaphore *sem, long *cntp) { - long cnt = atomic_long_add_return_acquire(RWSEM_READER_BIAS, &sem->count); + *cntp = atomic_long_add_return_acquire(RWSEM_READER_BIAS, &sem->count); - if (WARN_ON_ONCE(cnt < 0)) + if (WARN_ON_ONCE(*cntp < 0)) rwsem_set_nonspinnable(sem); - if (!(cnt & RWSEM_READ_FAILED_MASK)) { + if (!(*cntp & RWSEM_READ_FAILED_MASK)) { rwsem_set_reader_owned(sem); return true; } @@ -1008,9 +1008,9 @@ 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, long count, int state) { - long count, adjustment = -RWSEM_READER_BIAS; + long adjustment = -RWSEM_READER_BIAS; struct rwsem_waiter waiter; DEFINE_WAKE_Q(wake_q); bool wake = false; @@ -1356,8 +1356,10 @@ static struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem) */ static inline int __down_read_common(struct rw_semaphore *sem, int state) { - if (!rwsem_read_trylock(sem)) { - if (IS_ERR(rwsem_down_read_slowpath(sem, state))) + long count; + + if (!rwsem_read_trylock(sem, &count)) { + if (IS_ERR(rwsem_down_read_slowpath(sem, count, state))) return -EINTR; DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem); } -- 2.30.2