locking/mutex: clear MUTEX_FLAGS if wait_list is empty due to signal

When a interruptible mutex locker is interrupted by a signal
without acquiring this lock and removed from the wait queue.
if the mutex isn't contended enough to have a waiter
put into the wait queue again, the setting of the WAITER
bit will force mutex locker to go into the slowpath to
acquire the lock every time, so if the wait queue is empty,
the WAITER bit need to be clear.

Fixes: 040a0a3 ("mutex: Add support for wound/wait style locks")
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Zqiang <qiang.zhang@windriver.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210517034005.30828-1-qiang.zhang@windriver.com

kernel/locking/mutex-debug.c

@@ -57,15 +57,15 @@ void debug_mutex_add_waiter(struct mutex *lock, struct mutex_waiter *waiter,
 	task->blocked_on = waiter;
 }
 
-void mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *waiter,
+void debug_mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *waiter,
 			 struct task_struct *task)
 {
 	DEBUG_LOCKS_WARN_ON(list_empty(&waiter->list));
 	DEBUG_LOCKS_WARN_ON(waiter->task != task);
 	DEBUG_LOCKS_WARN_ON(task->blocked_on != waiter);
 	task->blocked_on = NULL;
 
-	list_del_init(&waiter->list);
+	INIT_LIST_HEAD(&waiter->list);
 	waiter->task = NULL;
 }
 

kernel/locking/mutex-debug.h

@@ -22,7 +22,7 @@ extern void debug_mutex_free_waiter(struct mutex_waiter *waiter);
 extern void debug_mutex_add_waiter(struct mutex *lock,
 				   struct mutex_waiter *waiter,
 				   struct task_struct *task);
-extern void mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *waiter,
+extern void debug_mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *waiter,
 				struct task_struct *task);
 extern void debug_mutex_unlock(struct mutex *lock);
 extern void debug_mutex_init(struct mutex *lock, const char *name,

kernel/locking/mutex.c

@@ -194,7 +194,7 @@ static inline bool __mutex_waiter_is_first(struct mutex *lock, struct mutex_wait
  * Add @waiter to a given location in the lock wait_list and set the
  * FLAG_WAITERS flag if it's the first waiter.
  */
-static void __sched
+static void
 __mutex_add_waiter(struct mutex *lock, struct mutex_waiter *waiter,
 		   struct list_head *list)
 {
@@ -205,6 +205,16 @@ __mutex_add_waiter(struct mutex *lock, struct mutex_waiter *waiter,
 		__mutex_set_flag(lock, MUTEX_FLAG_WAITERS);
 }
 
+static void
+__mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *waiter)
+{
+	list_del(&waiter->list);
+	if (likely(list_empty(&lock->wait_list)))
+		__mutex_clear_flag(lock, MUTEX_FLAGS);
+
+	debug_mutex_remove_waiter(lock, waiter, current);
+}
+
 /*
  * Give up ownership to a specific task, when @task = NULL, this is equivalent
  * to a regular unlock. Sets PICKUP on a handoff, clears HANDOFF, preserves
@@ -1061,9 +1071,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
 			__ww_mutex_check_waiters(lock, ww_ctx);
 	}
 
-	mutex_remove_waiter(lock, &waiter, current);
-	if (likely(list_empty(&lock->wait_list)))
-		__mutex_clear_flag(lock, MUTEX_FLAGS);
+	__mutex_remove_waiter(lock, &waiter);
 
 	debug_mutex_free_waiter(&waiter);
 
@@ -1080,7 +1088,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
 
 err:
 	__set_current_state(TASK_RUNNING);
-	mutex_remove_waiter(lock, &waiter, current);
+	__mutex_remove_waiter(lock, &waiter);
 err_early_kill:
 	spin_unlock(&lock->wait_lock);
 	debug_mutex_free_waiter(&waiter);

kernel/locking/mutex.h

@@ -10,12 +10,10 @@
  * !CONFIG_DEBUG_MUTEXES case. Most of them are NOPs:
  */
 
-#define mutex_remove_waiter(lock, waiter, task) \
-		__list_del((waiter)->list.prev, (waiter)->list.next)
-
 #define debug_mutex_wake_waiter(lock, waiter)		do { } while (0)
 #define debug_mutex_free_waiter(waiter)			do { } while (0)
 #define debug_mutex_add_waiter(lock, waiter, ti)	do { } while (0)
+#define debug_mutex_remove_waiter(lock, waiter, ti)     do { } while (0)
 #define debug_mutex_unlock(lock)			do { } while (0)
 #define debug_mutex_init(lock, name, key)		do { } while (0)