locking/lockdep: Fix hlock->pin_count reset on lock stack rebuilds

Various people reported hitting the "unpinning an unpinned lock"
warning. As it turns out there are 2 places where we take a lock out
of the middle of a stack, and in those cases it would fail to preserve
the pin_count when rebuilding the lock stack.

Reported-by: Sasha Levin <sasha.levin@oracle.com>
Reported-by: Tim Spriggs <tspriggs@apple.com>
Tested-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: davej@codemonkey.org.uk
Link: http://lkml.kernel.org/r/20150916141040.GA11639@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/locking/lockdep.c

@@ -3068,7 +3068,7 @@ static int __lock_is_held(struct lockdep_map *lock);
 static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
 			  int trylock, int read, int check, int hardirqs_off,
 			  struct lockdep_map *nest_lock, unsigned long ip,
-			  int references)
+			  int references, int pin_count)
 {
 	struct task_struct *curr = current;
 	struct lock_class *class = NULL;
@@ -3157,7 +3157,7 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
 	hlock->waittime_stamp = 0;
 	hlock->holdtime_stamp = lockstat_clock();
 #endif
-	hlock->pin_count = 0;
+	hlock->pin_count = pin_count;
 
 	if (check && !mark_irqflags(curr, hlock))
 		return 0;
@@ -3343,7 +3343,7 @@ found_it:
 			hlock_class(hlock)->subclass, hlock->trylock,
 				hlock->read, hlock->check, hlock->hardirqs_off,
 				hlock->nest_lock, hlock->acquire_ip,
-				hlock->references))
+				hlock->references, hlock->pin_count))
 			return 0;
 	}
 
@@ -3433,7 +3433,7 @@ found_it:
 			hlock_class(hlock)->subclass, hlock->trylock,
 				hlock->read, hlock->check, hlock->hardirqs_off,
 				hlock->nest_lock, hlock->acquire_ip,
-				hlock->references))
+				hlock->references, hlock->pin_count))
 			return 0;
 	}
 
@@ -3583,7 +3583,7 @@ void lock_acquire(struct lockdep_map *lock, unsigned int subclass,
 	current->lockdep_recursion = 1;
 	trace_lock_acquire(lock, subclass, trylock, read, check, nest_lock, ip);
 	__lock_acquire(lock, subclass, trylock, read, check,
-		       irqs_disabled_flags(flags), nest_lock, ip, 0);
+		       irqs_disabled_flags(flags), nest_lock, ip, 0, 0);
 	current->lockdep_recursion = 0;
 	raw_local_irq_restore(flags);
 }