dm block manager: cleanup code that prints stacktrace

There is no need to record stack trace and immediately print it.  Just
use dump_stack() to print the current stack.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/persistent-data/dm-block-manager.c

@@ -97,10 +97,6 @@ static void __del_holder(struct block_lock *lock, struct task_struct *task)
 static int __check_holder(struct block_lock *lock)
 {
 	unsigned i;
-#ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
-	static struct stack_trace t;
-	static stack_entries entries;
-#endif
 
 	for (i = 0; i < MAX_HOLDERS; i++) {
 		if (lock->holders[i] == current) {
@@ -110,12 +106,7 @@ static int __check_holder(struct block_lock *lock)
 			print_stack_trace(lock->traces + i, 4);
 
 			DMERR("subsequent acquisition attempted here:");
-			t.nr_entries = 0;
-			t.max_entries = MAX_STACK;
-			t.entries = entries;
-			t.skip = 3;
-			save_stack_trace(&t);
-			print_stack_trace(&t, 4);
+			dump_stack();
 #endif
 			return -EINVAL;
 		}