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);