[PATCH] locking/rwsem: Add up_write_non_owner() for percpu_up_write()

[Waiman Long]

The commit 8c5db92a705d ("locking/rwsem: Add DEBUG_RWSEMS to look for
lock/unlock mismatches") causes a warning in ext4 fstests due to the
fact that the freeze and thaw ioctls, by design, are run in different
processes. This is not a bug in the commit itself. Rather, we need a
up_write() variant that annotates the fact that it can be called from
a task different from the one that took the lock.

The new API is up_write_non_owner() and the percpu_up_write() function
is modified to use it instead of the plain up_write().

Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
---
 include/linux/rwsem.h         |  6 ++++++
 kernel/locking/percpu-rwsem.c |  4 +++-
 kernel/locking/rwsem.c        | 13 +++++++++++++
 3 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h
index 56707d5..0e2a425 100644
--- a/include/linux/rwsem.h
+++ b/include/linux/rwsem.h
@@ -187,4 +187,10 @@ static inline int rwsem_is_contended(struct rw_semaphore *sem)
 # define up_read_non_owner(sem)			up_read(sem)
 #endif
 
+#ifdef CONFIG_DEBUG_RWSEMS
+extern void up_write_non_owner(struct rw_semaphore *sem);
+#else
+# define up_write_non_owner(sem)	up_write(sem)
+#endif
+
 #endif /* _LINUX_RWSEM_H */
diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
index 883cf1b..13decf2 100644
--- a/kernel/locking/percpu-rwsem.c
+++ b/kernel/locking/percpu-rwsem.c
@@ -179,8 +179,10 @@ void percpu_up_write(struct percpu_rw_semaphore *sem)
 
 	/*
 	 * Release the write lock, this will allow readers back in the game.
+	 * percpu_up_write() may be called from a task different from the one
+	 * taking the lock.
 	 */
-	up_write(&sem->rw_sem);
+	up_write_non_owner(&sem->rw_sem);
 
 	/*
 	 * Once this completes (at least one RCU-sched grace period hence) the
diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index 30465a2..140d5ef 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -222,4 +222,17 @@ void up_read_non_owner(struct rw_semaphore *sem)
 
 #endif
 
+#ifdef CONFIG_DEBUG_RWSEMS
+/*
+ * release a write lock from a different task
+ */
+void up_write_non_owner(struct rw_semaphore *sem)
+{
+	rwsem_release(&sem->dep_map, 1, _RET_IP_);
+	DEBUG_RWSEMS_WARN_ON(!sem->owner || (sem->owner == RWSEM_READER_OWNED));
 
+	rwsem_clear_owner(sem);
+	__up_write(sem);
+}
+EXPORT_SYMBOL(up_write_non_owner);
+#endif
-- 
1.8.3.1