From 403d5d1318c9b82b70c44a76e3ddbadf42a7838a Mon Sep 17 00:00:00 2001
From: xieliujie <xieliujie@oppo.com>
Date: Tue, 6 Jun 2023 20:45:12 +0800
Subject: [PATCH] ANDROID: vendor_hook: Avoid clearing protect-flag before
 waking waiters

With hooks below, we can mark a lock-owned thread with an identifiable flag, which can protect it from being preempted by some other unimportant threads, and then waiter will be wakeup more quickly.
https://android-review.googlesource.com/c/kernel/common/+/2183353

but now we find an issue like this one:
static inline void __up_write(struct rw_semaphore *sem)
{
        ...
        // Step 1. we clear flag.
        trace_android_vh_record_rwsem_lock_starttime(current, 0);
        // Step 2. owner may be preempted by unimportant threads.
        rwsem_clear_owner(sem);
        ...
        // Step 3. wake up waiter, but it's too later.
        if (unlikely(tmp & RWSEM_FLAG_WAITERS))
                rwsem_wake(sem);
}

This patch will clear protect-flag after waking up waiters.

Bug: 286024926
Change-Id: I71f8b6a7d8a01336fd36b8267c2cb5edab65bd11
Signed-off-by: xieliujie <xieliujie@oppo.com>
---
 include/linux/percpu-rwsem.h  | 2 +-
 kernel/locking/mutex.c        | 2 +-
 kernel/locking/percpu-rwsem.c | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/linux/percpu-rwsem.h b/include/linux/percpu-rwsem.h
index 92d172cfce06..55e80d18628d 100644
--- a/include/linux/percpu-rwsem.h
+++ b/include/linux/percpu-rwsem.h
@@ -107,7 +107,6 @@ static inline bool percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
 
 static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
 {
-	_trace_android_vh_record_pcpu_rwsem_starttime(current, 0);
 	rwsem_release(&sem->dep_map, _RET_IP_);
 
 	preempt_disable();
@@ -130,6 +129,7 @@ static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
 		this_cpu_dec(*sem->read_count);
 		rcuwait_wake_up(&sem->writer);
 	}
+	_trace_android_vh_record_pcpu_rwsem_starttime(current, 0);
 	preempt_enable();
 }
 
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index b9a10aacb139..be121ed70d7c 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -760,12 +760,12 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
  */
 void __sched mutex_unlock(struct mutex *lock)
 {
-	trace_android_vh_record_mutex_lock_starttime(current, 0);
 #ifndef CONFIG_DEBUG_LOCK_ALLOC
 	if (__mutex_unlock_fast(lock))
 		return;
 #endif
 	__mutex_unlock_slowpath(lock, _RET_IP_);
+	trace_android_vh_record_mutex_lock_starttime(current, 0);
 }
 EXPORT_SYMBOL(mutex_unlock);
 
diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
index c8a474aa1b3b..915c045a15f3 100644
--- a/kernel/locking/percpu-rwsem.c
+++ b/kernel/locking/percpu-rwsem.c
@@ -258,7 +258,6 @@ EXPORT_SYMBOL_GPL(percpu_down_write);
 
 void percpu_up_write(struct percpu_rw_semaphore *sem)
 {
-	trace_android_vh_record_pcpu_rwsem_starttime(current, 0);
 	rwsem_release(&sem->dep_map, _RET_IP_);
 
 	/*
@@ -284,6 +283,7 @@ void percpu_up_write(struct percpu_rw_semaphore *sem)
 	 * exclusive write lock because its counting.
 	 */
 	rcu_sync_exit(&sem->rss);
+	trace_android_vh_record_pcpu_rwsem_starttime(current, 0);
 }
 EXPORT_SYMBOL_GPL(percpu_up_write);