locking/mutex: Fix lockdep_assert_held() fail

In commit:

  659cf9f ("locking/ww_mutex: Optimize ww-mutexes by waking at most one waiter for backoff when acquiring the lock")

I replaced a comment with a lockdep_assert_held(). However it turns out
we hide that lock from lockdep for hysterical raisins, which results
in the assertion always firing.

Remove the old debug code as lockdep will easily spot the abuse it was
meant to catch, which will make the lock visible to lockdep and make
the assertion work as intended.

Reported-by: Mike Galbraith <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Nicolai Haehnle <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Fixes: 659cf9f ("locking/ww_mutex: Optimize ww-mutexes by waking at most one waiter for backoff when acquiring the lock")
Link: http://lkml.kernel.org/r/20170117150609.GB32474@worktop
Signed-off-by: Ingo Molnar <[email protected]>

Author: Peter Zijlstra

kernel/locking/mutex-debug.h

@@ -26,20 +26,3 @@ extern void mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *waiter,
 extern void debug_mutex_unlock(struct mutex *lock);
 extern void debug_mutex_init(struct mutex *lock, const char *name,
 			     struct lock_class_key *key);
-
-#define spin_lock_mutex(lock, flags)			\
-	do {						\
-		struct mutex *l = container_of(lock, struct mutex, wait_lock); \
-							\
-		DEBUG_LOCKS_WARN_ON(in_interrupt());	\
-		local_irq_save(flags);			\
-		arch_spin_lock(&(lock)->rlock.raw_lock);\
-		DEBUG_LOCKS_WARN_ON(l->magic != l);	\
-	} while (0)
-
-#define spin_unlock_mutex(lock, flags)				\
-	do {							\
-		arch_spin_unlock(&(lock)->rlock.raw_lock);	\
-		local_irq_restore(flags);			\
-		preempt_check_resched();			\
-	} while (0)

kernel/locking/mutex.c

@@ -325,8 +325,6 @@ __ww_mutex_wakeup_for_backoff(struct mutex *lock, struct ww_acquire_ctx *ww_ctx)
 static __always_inline void
 ww_mutex_set_context_fastpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 {
-	unsigned long flags;
-
 	ww_mutex_lock_acquired(lock, ctx);
 
 	lock->ctx = ctx;
@@ -350,9 +348,9 @@ ww_mutex_set_context_fastpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 	 * Uh oh, we raced in fastpath, wake up everyone in this case,
 	 * so they can see the new lock->ctx.
 	 */
-	spin_lock_mutex(&lock->base.wait_lock, flags);
+	spin_lock(&lock->base.wait_lock);
 	__ww_mutex_wakeup_for_backoff(&lock->base, ctx);
-	spin_unlock_mutex(&lock->base.wait_lock, flags);
+	spin_unlock(&lock->base.wait_lock);
 }
 
 /*
@@ -740,7 +738,6 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
 		    struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)
 {
 	struct mutex_waiter waiter;
-	unsigned long flags;
 	bool first = false;
 	struct ww_mutex *ww;
 	int ret;
@@ -766,7 +763,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
 		return 0;
 	}
 
-	spin_lock_mutex(&lock->wait_lock, flags);
+	spin_lock(&lock->wait_lock);
 	/*
 	 * After waiting to acquire the wait_lock, try again.
 	 */
@@ -830,7 +827,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
 				goto err;
 		}
 
-		spin_unlock_mutex(&lock->wait_lock, flags);
+		spin_unlock(&lock->wait_lock);
 		schedule_preempt_disabled();
 
 		/*
@@ -853,9 +850,9 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
 		    (first && mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, &waiter)))
 			break;
 
-		spin_lock_mutex(&lock->wait_lock, flags);
+		spin_lock(&lock->wait_lock);
 	}
-	spin_lock_mutex(&lock->wait_lock, flags);
+	spin_lock(&lock->wait_lock);
 acquired:
 	__set_current_state(TASK_RUNNING);
 
@@ -872,15 +869,15 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
 	if (use_ww_ctx && ww_ctx)
 		ww_mutex_set_context_slowpath(ww, ww_ctx);
 
-	spin_unlock_mutex(&lock->wait_lock, flags);
+	spin_unlock(&lock->wait_lock);
 	preempt_enable();
 	return 0;
 
 err:
 	__set_current_state(TASK_RUNNING);
 	mutex_remove_waiter(lock, &waiter, current);
 err_early_backoff:
-	spin_unlock_mutex(&lock->wait_lock, flags);
+	spin_unlock(&lock->wait_lock);
 	debug_mutex_free_waiter(&waiter);
 	mutex_release(&lock->dep_map, 1, ip);
 	preempt_enable();
@@ -999,8 +996,8 @@ EXPORT_SYMBOL_GPL(ww_mutex_lock_interruptible);
 static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip)
 {
 	struct task_struct *next = NULL;
-	unsigned long owner, flags;
 	DEFINE_WAKE_Q(wake_q);
+	unsigned long owner;
 
 	mutex_release(&lock->dep_map, 1, ip);
 
@@ -1035,7 +1032,7 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
 		owner = old;
 	}
 
-	spin_lock_mutex(&lock->wait_lock, flags);
+	spin_lock(&lock->wait_lock);
 	debug_mutex_unlock(lock);
 	if (!list_empty(&lock->wait_list)) {
 		/* get the first entry from the wait-list: */
@@ -1052,7 +1049,7 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
 	if (owner & MUTEX_FLAG_HANDOFF)
 		__mutex_handoff(lock, next);
 
-	spin_unlock_mutex(&lock->wait_lock, flags);
+	spin_unlock(&lock->wait_lock);
 
 	wake_up_q(&wake_q);
 }

kernel/locking/mutex.h

@@ -9,10 +9,6 @@
  * !CONFIG_DEBUG_MUTEXES case. Most of them are NOPs:
  */
 
-#define spin_lock_mutex(lock, flags) \
-		do { spin_lock(lock); (void)(flags); } while (0)
-#define spin_unlock_mutex(lock, flags) \
-		do { spin_unlock(lock); (void)(flags); } while (0)
 #define mutex_remove_waiter(lock, waiter, task) \
 		__list_del((waiter)->list.prev, (waiter)->list.next)