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Diffstat (limited to 'kernel/locking/rwsem.c')
-rw-r--r--kernel/locking/rwsem.c87
1 files changed, 52 insertions, 35 deletions
diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index 44873594de03..acb5a50309a1 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -256,16 +256,13 @@ static inline bool rwsem_read_trylock(struct rw_semaphore *sem, long *cntp)
static inline bool rwsem_write_trylock(struct rw_semaphore *sem)
{
long tmp = RWSEM_UNLOCKED_VALUE;
- bool ret = false;
- preempt_disable();
if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp, RWSEM_WRITER_LOCKED)) {
rwsem_set_owner(sem);
- ret = true;
+ return true;
}
- preempt_enable();
- return ret;
+ return false;
}
/*
@@ -624,18 +621,16 @@ static inline bool rwsem_try_write_lock(struct rw_semaphore *sem,
*/
if (first->handoff_set && (waiter != first))
return false;
-
- /*
- * First waiter can inherit a previously set handoff
- * bit and spin on rwsem if lock acquisition fails.
- */
- if (waiter == first)
- waiter->handoff_set = true;
}
new = count;
if (count & RWSEM_LOCK_MASK) {
+ /*
+ * A waiter (first or not) can set the handoff bit
+ * if it is an RT task or wait in the wait queue
+ * for too long.
+ */
if (has_handoff || (!rt_task(waiter->task) &&
!time_after(jiffies, waiter->timeout)))
return false;
@@ -651,11 +646,12 @@ static inline bool rwsem_try_write_lock(struct rw_semaphore *sem,
} while (!atomic_long_try_cmpxchg_acquire(&sem->count, &count, new));
/*
- * We have either acquired the lock with handoff bit cleared or
- * set the handoff bit.
+ * We have either acquired the lock with handoff bit cleared or set
+ * the handoff bit. Only the first waiter can have its handoff_set
+ * set here to enable optimistic spinning in slowpath loop.
*/
if (new & RWSEM_FLAG_HANDOFF) {
- waiter->handoff_set = true;
+ first->handoff_set = true;
lockevent_inc(rwsem_wlock_handoff);
return false;
}
@@ -717,7 +713,6 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
return false;
}
- preempt_disable();
/*
* Disable preemption is equal to the RCU read-side crital section,
* thus the task_strcut structure won't go away.
@@ -729,7 +724,6 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
if ((flags & RWSEM_NONSPINNABLE) ||
(owner && !(flags & RWSEM_READER_OWNED) && !owner_on_cpu(owner)))
ret = false;
- preempt_enable();
lockevent_cond_inc(rwsem_opt_fail, !ret);
return ret;
@@ -829,8 +823,6 @@ static bool rwsem_optimistic_spin(struct rw_semaphore *sem)
int loop = 0;
u64 rspin_threshold = 0;
- preempt_disable();
-
/* sem->wait_lock should not be held when doing optimistic spinning */
if (!osq_lock(&sem->osq))
goto done;
@@ -938,7 +930,6 @@ static bool rwsem_optimistic_spin(struct rw_semaphore *sem)
}
osq_unlock(&sem->osq);
done:
- preempt_enable();
lockevent_cond_inc(rwsem_opt_fail, !taken);
return taken;
}
@@ -1092,7 +1083,7 @@ queue:
/* Ordered by sem->wait_lock against rwsem_mark_wake(). */
break;
}
- schedule();
+ schedule_preempt_disabled();
lockevent_inc(rwsem_sleep_reader);
}
@@ -1179,15 +1170,12 @@ rwsem_down_write_slowpath(struct rw_semaphore *sem, int state)
if (waiter.handoff_set) {
enum owner_state owner_state;
- preempt_disable();
owner_state = rwsem_spin_on_owner(sem);
- preempt_enable();
-
if (owner_state == OWNER_NULL)
goto trylock_again;
}
- schedule();
+ schedule_preempt_disabled();
lockevent_inc(rwsem_sleep_writer);
set_current_state(state);
trylock_again:
@@ -1254,14 +1242,20 @@ static struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem)
*/
static inline int __down_read_common(struct rw_semaphore *sem, int state)
{
+ int ret = 0;
long count;
+ preempt_disable();
if (!rwsem_read_trylock(sem, &count)) {
- if (IS_ERR(rwsem_down_read_slowpath(sem, count, state)))
- return -EINTR;
+ if (IS_ERR(rwsem_down_read_slowpath(sem, count, state))) {
+ ret = -EINTR;
+ goto out;
+ }
DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
}
- return 0;
+out:
+ preempt_enable();
+ return ret;
}
static inline void __down_read(struct rw_semaphore *sem)
@@ -1281,19 +1275,23 @@ static inline int __down_read_killable(struct rw_semaphore *sem)
static inline int __down_read_trylock(struct rw_semaphore *sem)
{
+ int ret = 0;
long tmp;
DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
+ preempt_disable();
tmp = atomic_long_read(&sem->count);
while (!(tmp & RWSEM_READ_FAILED_MASK)) {
if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
tmp + RWSEM_READER_BIAS)) {
rwsem_set_reader_owned(sem);
- return 1;
+ ret = 1;
+ break;
}
}
- return 0;
+ preempt_enable();
+ return ret;
}
/*
@@ -1301,12 +1299,15 @@ static inline int __down_read_trylock(struct rw_semaphore *sem)
*/
static inline int __down_write_common(struct rw_semaphore *sem, int state)
{
+ int ret = 0;
+
+ preempt_disable();
if (unlikely(!rwsem_write_trylock(sem))) {
if (IS_ERR(rwsem_down_write_slowpath(sem, state)))
- return -EINTR;
+ ret = -EINTR;
}
-
- return 0;
+ preempt_enable();
+ return ret;
}
static inline void __down_write(struct rw_semaphore *sem)
@@ -1321,8 +1322,14 @@ static inline int __down_write_killable(struct rw_semaphore *sem)
static inline int __down_write_trylock(struct rw_semaphore *sem)
{
+ int ret;
+
+ preempt_disable();
DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
- return rwsem_write_trylock(sem);
+ ret = rwsem_write_trylock(sem);
+ preempt_enable();
+
+ return ret;
}
/*
@@ -1335,6 +1342,7 @@ static inline void __up_read(struct rw_semaphore *sem)
DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
+ preempt_disable();
rwsem_clear_reader_owned(sem);
tmp = atomic_long_add_return_release(-RWSEM_READER_BIAS, &sem->count);
DEBUG_RWSEMS_WARN_ON(tmp < 0, sem);
@@ -1343,6 +1351,7 @@ static inline void __up_read(struct rw_semaphore *sem)
clear_nonspinnable(sem);
rwsem_wake(sem);
}
+ preempt_enable();
}
/*
@@ -1363,9 +1372,9 @@ static inline void __up_write(struct rw_semaphore *sem)
preempt_disable();
rwsem_clear_owner(sem);
tmp = atomic_long_fetch_add_release(-RWSEM_WRITER_LOCKED, &sem->count);
- preempt_enable();
if (unlikely(tmp & RWSEM_FLAG_WAITERS))
rwsem_wake(sem);
+ preempt_enable();
}
/*
@@ -1383,11 +1392,13 @@ static inline void __downgrade_write(struct rw_semaphore *sem)
* write side. As such, rely on RELEASE semantics.
*/
DEBUG_RWSEMS_WARN_ON(rwsem_owner(sem) != current, sem);
+ preempt_disable();
tmp = atomic_long_fetch_add_release(
-RWSEM_WRITER_LOCKED+RWSEM_READER_BIAS, &sem->count);
rwsem_set_reader_owned(sem);
if (tmp & RWSEM_FLAG_WAITERS)
rwsem_downgrade_wake(sem);
+ preempt_enable();
}
#else /* !CONFIG_PREEMPT_RT */
@@ -1662,6 +1673,12 @@ void down_read_non_owner(struct rw_semaphore *sem)
{
might_sleep();
__down_read(sem);
+ /*
+ * The owner value for a reader-owned lock is mostly for debugging
+ * purpose only and is not critical to the correct functioning of
+ * rwsem. So it is perfectly fine to set it in a preempt-enabled
+ * context here.
+ */
__rwsem_set_reader_owned(sem, NULL);
}
EXPORT_SYMBOL(down_read_non_owner);