ANDROID: vendor_hooks: Add android_vh_rwsem_downgrade_wake_finish to rwsem_downgrade_wake

The commit d4528a28cb5b ("ANDROID: vendor_hooks: Add hooks for
rwsem and mutex") adds the android_vh_rwsem_wake_finish hook to
rwsem_wake().It can get the point when a [write/read]_owner
releases the rwsem and wakes up other waiters of the rwsem.
However, it cannot cover a scenario that a task acquires the
write-lock first, then downgrades to the read-lock and wakes up
other waiters in list.

In order to avoid breaking other partner handlers that don't
expect to be called from rwsem_downgrade_wake,this patch adds
a new vendor hook named android_vh_rwsem_downgrade_wake_finish
to rwsem_downgrade_wake() as Todd Kjos suggested.

Bug: 319178409
Change-Id: I73f677d2aa813777f21f13fafc17b1f912f6ef7e
Signed-off-by: Jing Xia <jing.xia@unisoc.com>
(cherry picked from commit 6ac0a2682b5f958c7204506e58b67ffebb06ad85)

drivers/android/vendor_hooks.c

@@ -146,3 +146,4 @@ EXPORT_TRACEPOINT_SYMBOL_GPL(android_vh_rwsem_init);
 EXPORT_TRACEPOINT_SYMBOL_GPL(android_vh_rwsem_wake);
 EXPORT_TRACEPOINT_SYMBOL_GPL(android_vh_rwsem_write_finished);
 EXPORT_TRACEPOINT_SYMBOL_GPL(android_vh_alter_rwsem_list_add);
+EXPORT_TRACEPOINT_SYMBOL_GPL(android_vh_rwsem_downgrade_wake_finish);

include/trace/hooks/rwsem.h

@@ -25,6 +25,9 @@ DECLARE_HOOK(android_vh_alter_rwsem_list_add,
 		 struct rw_semaphore *sem,
 		 bool *already_on_list),
 	TP_ARGS(waiter, sem, already_on_list));
+DECLARE_HOOK(android_vh_rwsem_downgrade_wake_finish,
+	TP_PROTO(struct rw_semaphore *sem),
+	TP_ARGS(sem));
 #endif /* _TRACE_HOOK_RWSEM_H */
 /* This part must be outside protection */
 #include <trace/define_trace.h>

kernel/locking/rwsem.c

@@ -1250,6 +1250,8 @@ static struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem)
 	if (!list_empty(&sem->wait_list))
 		rwsem_mark_wake(sem, RWSEM_WAKE_READ_OWNED, &wake_q);
 
+	trace_android_vh_rwsem_downgrade_wake_finish(sem);
+
 	raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
 	wake_up_q(&wake_q);