From 3a010c493271f04578b133de977e0e5dd2848cea Mon Sep 17 00:00:00 2001
From: Zqiang <qiang.zhang@windriver.com>
Date: Mon, 17 May 2021 11:40:05 +0800
Subject: [PATCH] locking/mutex: clear MUTEX_FLAGS if wait_list is empty due to signal
Git-commit: 3a010c493271f04578b133de977e0e5dd2848cea
Patch-mainline: v5.13-rc1
References: git-fixes

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: 040a0a371005 ("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
Signed-off-by: Davidlohr Bueso <dbueso@suse.de> 

---
 kernel/locking/mutex-debug.c |  4 ++--
 kernel/locking/mutex-debug.h |  2 +-
 kernel/locking/mutex.c       | 16 ++++++++++++----
 kernel/locking/mutex.h       |  4 +---
 4 files changed, 16 insertions(+), 10 deletions(-)

diff --git a/kernel/locking/mutex-debug.c b/kernel/locking/mutex-debug.c
index 9aa713629387..839df4383799 100644
--- a/kernel/locking/mutex-debug.c
+++ b/kernel/locking/mutex-debug.c
@@ -57,7 +57,7 @@ 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));
@@ -65,7 +65,7 @@ void mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *waiter,
 	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;
 }
 
diff --git a/kernel/locking/mutex-debug.h b/kernel/locking/mutex-debug.h
index 4174417d5309..660e901b2922 100644
--- a/kernel/locking/mutex-debug.h
+++ b/kernel/locking/mutex-debug.h
@@ -21,7 +21,7 @@ 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,
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index 198527a62149..bad6aa154912 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -172,6 +172,16 @@ static inline bool __mutex_waiter_is_first(struct mutex *lock, struct mutex_wait
 	return list_first_entry(&lock->wait_list, struct mutex_waiter, list) == waiter;
 }
 
+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 HANDOF, preserves
@@ -858,9 +868,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
 acquired:
 	__set_current_state(TASK_RUNNING);
 
-	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);
 
@@ -877,7 +885,7 @@ __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_backoff:
 	spin_unlock(&lock->wait_lock);
 	debug_mutex_free_waiter(&waiter);
diff --git a/kernel/locking/mutex.h b/kernel/locking/mutex.h
index 6ebc1902f779..7d0554f5aaa1 100644
--- a/kernel/locking/mutex.h
+++ b/kernel/locking/mutex.h
@@ -9,12 +9,10 @@
  * !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)
 
--
2.26.2