dm target: use module refcount directly

The tt_internal's 'use' field is superfluous: the module's refcount can do
the work properly.  An acceptable side-effect is that this increases the
reference counts reported by 'lsmod'.

Remove the superfluous test when removing a target module.

[Crash possible without this on SMP - agk]

Cc: stable@kernel.org
Signed-off-by: Cheng Renquan <crquan@gmail.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Reviewed-by: Alasdair G Kergon <agk@redhat.com>
Reviewed-by: Jonathan Brassow <jbrassow@redhat.com>

drivers/md/dm-target.c

@@ -18,7 +18,6 @@ struct tt_internal {
 	struct target_type tt;
 
 	struct list_head list;
-	long use;
 };
 
 static LIST_HEAD(_targets);
@@ -44,12 +43,8 @@ static struct tt_internal *get_target_type(const char *name)
 	down_read(&_lock);
 
 	ti = __find_target_type(name);
-	if (ti) {
-		if ((ti->use == 0) && !try_module_get(ti->tt.module))
+	if (ti && !try_module_get(ti->tt.module))
 		ti = NULL;
-		else
-			ti->use++;
-	}
 
 	up_read(&_lock);
 	return ti;
@@ -77,10 +72,7 @@ void dm_put_target_type(struct target_type *t)
 	struct tt_internal *ti = (struct tt_internal *) t;
 
 	down_read(&_lock);
-	if (--ti->use == 0)
 	module_put(ti->tt.module);
-
-	BUG_ON(ti->use < 0);
 	up_read(&_lock);
 
 	return;
@@ -140,12 +132,6 @@ void dm_unregister_target(struct target_type *t)
 		BUG();
 	}
 
-	if (ti->use) {
-		DMCRIT("Attempt to unregister target still in use: %s",
-		       t->name);
-		BUG();
-	}
-
 	list_del(&ti->list);
 	kfree(ti);