[PATCH-tip v2 06/10] locking/rwsem: Enhance DEBUG_RWSEMS_WARN_ON() macro

[Waiman Long]

Currently, the DEBUG_RWSEMS_WARN_ON() macro just dumps a stack trace
when the rwsem isn't in the right state. It does not show the actual
states of the rwsem. This may not be that helpful in the debugging
process.

Enhance the DEBUG_RWSEMS_WARN_ON() macro to also show the current
content of the rwsem count and owner fields to give more information
about what is wrong with the rwsem.

Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
---
 kernel/locking/rwsem.c |  3 ++-
 kernel/locking/rwsem.h | 19 ++++++++++++-------
 2 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index 90de5f1..ccbf18f 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -198,7 +198,8 @@ int __sched down_write_killable_nested(struct rw_semaphore *sem, int subclass)
 
 void up_read_non_owner(struct rw_semaphore *sem)
 {
-	DEBUG_RWSEMS_WARN_ON(!((unsigned long)sem->owner & RWSEM_READER_OWNED));
+	DEBUG_RWSEMS_WARN_ON(!((unsigned long)sem->owner & RWSEM_READER_OWNED),
+				sem);
 	__up_read(sem);
 }
 
diff --git a/kernel/locking/rwsem.h b/kernel/locking/rwsem.h
index 1d8f722..c8fd3f1 100644
--- a/kernel/locking/rwsem.h
+++ b/kernel/locking/rwsem.h
@@ -27,9 +27,13 @@
 #define RWSEM_ANONYMOUSLY_OWNED	(1UL << 1)
 
 #ifdef CONFIG_DEBUG_RWSEMS
-# define DEBUG_RWSEMS_WARN_ON(c)	DEBUG_LOCKS_WARN_ON(c)
+# define DEBUG_RWSEMS_WARN_ON(c, sem)				\
+	WARN_ONCE(c, "DEBUG_RWSEMS_WARN_ON(%s): count = 0x%lx, owner = 0x%lx, curr 0x%lx, list %sempty\n",\
+		#c, atomic_long_read(&(sem)->count),		\
+		(long)((sem)->owner), (long)current,		\
+		list_empty(&(sem)->wait_list) ? "" : "not ")
 #else
-# define DEBUG_RWSEMS_WARN_ON(c)
+# define DEBUG_RWSEMS_WARN_ON(c, sem)
 #endif
 
 /*
@@ -168,7 +172,7 @@ static inline void __down_read(struct rw_semaphore *sem)
 	if (unlikely(atomic_long_inc_return_acquire(&sem->count) <= 0)) {
 		rwsem_down_read_failed(sem);
 		DEBUG_RWSEMS_WARN_ON(!((unsigned long)sem->owner &
-					RWSEM_READER_OWNED));
+					RWSEM_READER_OWNED), sem);
 	} else {
 		rwsem_set_reader_owned(sem);
 	}
@@ -180,7 +184,7 @@ static inline int __down_read_killable(struct rw_semaphore *sem)
 		if (IS_ERR(rwsem_down_read_failed_killable(sem)))
 			return -EINTR;
 		DEBUG_RWSEMS_WARN_ON(!((unsigned long)sem->owner &
-					RWSEM_READER_OWNED));
+					RWSEM_READER_OWNED), sem);
 	} else {
 		rwsem_set_reader_owned(sem);
 	}
@@ -251,7 +255,8 @@ static inline void __up_read(struct rw_semaphore *sem)
 {
 	long tmp;
 
-	DEBUG_RWSEMS_WARN_ON(!((unsigned long)sem->owner & RWSEM_READER_OWNED));
+	DEBUG_RWSEMS_WARN_ON(!((unsigned long)sem->owner & RWSEM_READER_OWNED),
+				sem);
 	rwsem_clear_reader_owned(sem);
 	tmp = atomic_long_dec_return_release(&sem->count);
 	if (unlikely(tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0))
@@ -263,7 +268,7 @@ static inline void __up_read(struct rw_semaphore *sem)
  */
 static inline void __up_write(struct rw_semaphore *sem)
 {
-	DEBUG_RWSEMS_WARN_ON(sem->owner != current);
+	DEBUG_RWSEMS_WARN_ON(sem->owner != current, sem);
 	rwsem_clear_owner(sem);
 	if (unlikely(atomic_long_sub_return_release(RWSEM_ACTIVE_WRITE_BIAS,
 						    &sem->count) < 0))
@@ -284,7 +289,7 @@ static inline void __downgrade_write(struct rw_semaphore *sem)
 	 * read-locked region is ok to be re-ordered into the
 	 * write side. As such, rely on RELEASE semantics.
 	 */
-	DEBUG_RWSEMS_WARN_ON(sem->owner != current);
+	DEBUG_RWSEMS_WARN_ON(sem->owner != current, sem);
 	tmp = atomic_long_add_return_release(-RWSEM_WAITING_BIAS, &sem->count);
 	rwsem_set_reader_owned(sem);
 	if (tmp < 0)
-- 
1.8.3.1