Before combining owner and count, we are adding two new helpers for accessing the owner value in the rwsem.
1) struct task_struct *rwsem_get_owner(struct rw_semaphore *sem) 2) bool is_rwsem_reader_owned(struct rw_semaphore *sem) Signed-off-by: Waiman Long <long...@redhat.com> --- kernel/locking/rwsem.c | 50 +++++++++++++++++++++++++++++++----------- 1 file changed, 37 insertions(+), 13 deletions(-) diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c index 8b23009e6b2c..ab26aba65371 100644 --- a/kernel/locking/rwsem.c +++ b/kernel/locking/rwsem.c @@ -130,6 +130,11 @@ static inline void rwsem_clear_owner(struct rw_semaphore *sem) WRITE_ONCE(sem->owner, NULL); } +static inline struct task_struct *rwsem_get_owner(struct rw_semaphore *sem) +{ + return READ_ONCE(sem->owner); +} + /* * The task_struct pointer of the last owning reader will be left in * the owner field. @@ -174,6 +179,23 @@ static inline bool is_rwsem_spinnable(struct rw_semaphore *sem) return is_rwsem_owner_spinnable(READ_ONCE(sem->owner)); } +/* + * Return true if the rwsem is owned by a reader. + */ +static inline bool is_rwsem_reader_owned(struct rw_semaphore *sem) +{ +#ifdef CONFIG_DEBUG_RWSEMS + /* + * Check the count to see if it is write-locked. + */ + long count = atomic_long_read(&sem->count); + + if (count & RWSEM_WRITER_MASK) + return false; +#endif + return (unsigned long)sem->owner & RWSEM_READER_OWNED; +} + /* * Return true if rwsem is owned by an anonymous writer or readers. */ @@ -193,6 +215,7 @@ static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem) { unsigned long val = (unsigned long)current | RWSEM_READER_OWNED | RWSEM_ANONYMOUSLY_OWNED; + if (READ_ONCE(sem->owner) == (struct task_struct *)val) cmpxchg_relaxed((unsigned long *)&sem->owner, val, RWSEM_READER_OWNED | RWSEM_ANONYMOUSLY_OWNED); @@ -530,7 +553,7 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem) preempt_disable(); rcu_read_lock(); - owner = READ_ONCE(sem->owner); + owner = rwsem_get_owner(sem); if (owner) { ret = is_rwsem_owner_spinnable(owner) && (is_rwsem_owner_reader(owner) || owner_on_cpu(owner)); @@ -562,15 +585,21 @@ enum owner_state { static noinline enum owner_state rwsem_spin_on_owner(struct rw_semaphore *sem) { - struct task_struct *owner = READ_ONCE(sem->owner); + struct task_struct *owner = rwsem_get_owner(sem); long count; if (!is_rwsem_owner_spinnable(owner)) return OWNER_NONSPINNABLE; rcu_read_lock(); - while (owner && !is_rwsem_owner_reader(owner) - && (READ_ONCE(sem->owner) == owner)) { + while (owner && !is_rwsem_owner_reader(owner)) { + struct task_struct *new_owner = rwsem_get_owner(sem); + + if (new_owner != owner) { + owner = new_owner; + break; /* The owner has changed */ + } + /* * Ensure we emit the owner->on_cpu, dereference _after_ * checking sem->owner still matches owner, if that fails, @@ -597,7 +626,6 @@ static noinline enum owner_state rwsem_spin_on_owner(struct rw_semaphore *sem) * spinning except when here is no active locks and the handoff bit * is set. In this case, we have to stop spinning. */ - owner = READ_ONCE(sem->owner); if (!is_rwsem_owner_spinnable(owner)) return OWNER_NONSPINNABLE; if (owner && !is_rwsem_owner_reader(owner)) @@ -1093,8 +1121,7 @@ inline void __down_read(struct rw_semaphore *sem) if (unlikely(atomic_long_fetch_add_acquire(RWSEM_READER_BIAS, &sem->count) & RWSEM_READ_FAILED_MASK)) { rwsem_down_read_failed(sem); - DEBUG_RWSEMS_WARN_ON(!((unsigned long)sem->owner & - RWSEM_READER_OWNED), sem); + DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem); } else { rwsem_set_reader_owned(sem); } @@ -1106,8 +1133,7 @@ static inline int __down_read_killable(struct rw_semaphore *sem) &sem->count) & RWSEM_READ_FAILED_MASK)) { if (IS_ERR(rwsem_down_read_failed_killable(sem))) return -EINTR; - DEBUG_RWSEMS_WARN_ON(!((unsigned long)sem->owner & - RWSEM_READER_OWNED), sem); + DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem); } else { rwsem_set_reader_owned(sem); } @@ -1174,8 +1200,7 @@ inline void __up_read(struct rw_semaphore *sem) { long tmp; - DEBUG_RWSEMS_WARN_ON(!((unsigned long)sem->owner & RWSEM_READER_OWNED), - sem); + DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem); rwsem_clear_reader_owned(sem); tmp = atomic_long_add_return_release(-RWSEM_READER_BIAS, &sem->count); if (unlikely((tmp & (RWSEM_LOCK_MASK|RWSEM_FLAG_WAITERS)) @@ -1382,8 +1407,7 @@ EXPORT_SYMBOL(down_write_killable_nested); void up_read_non_owner(struct rw_semaphore *sem) { - DEBUG_RWSEMS_WARN_ON(!((unsigned long)sem->owner & RWSEM_READER_OWNED), - sem); + DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem); __up_read(sem); } EXPORT_SYMBOL(up_read_non_owner); -- 2.18.1