stm class: Fix device leak in open error path

Make sure to drop the reference taken by class_find_device() also on
allocation errors in open().
Signed-off-by: Johan Hovold <johan@kernel.org>
Fixes: 7bd1d409 ("stm class: Introduce an abstraction for...")
Cc: stable@vger.kernel.org # v4.6+
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>

drivers/hwtracing/stm/core.c

@@ -361,7 +361,7 @@ static int stm_char_open(struct inode *inode, struct file *file)
 	struct stm_file *stmf;
 	struct device *dev;
 	unsigned int major = imajor(inode);
-	int err = -ENODEV;
+	int err = -ENOMEM;
 
 	dev = class_find_device(&stm_class, NULL, &major, major_match);
 	if (!dev)
@@ -369,8 +369,9 @@ static int stm_char_open(struct inode *inode, struct file *file)
 
 	stmf = kzalloc(sizeof(*stmf), GFP_KERNEL);
 	if (!stmf)
-		return -ENOMEM;
+		goto err_put_device;
 
+	err = -ENODEV;
 	stm_output_init(&stmf->output);
 	stmf->stm = to_stm_device(dev);
 
@@ -382,9 +383,10 @@ static int stm_char_open(struct inode *inode, struct file *file)
 	return nonseekable_open(inode, file);
 
 err_free:
+	kfree(stmf);
+err_put_device:
 	/* matches class_find_device() above */
 	put_device(dev);
-	kfree(stmf);
 
 	return err;
 }