md: tidy up error paths in md_alloc

As the recent bug in md_alloc showed, having a single exit path for
unlocking and putting is a good idea.  So restructure md_alloc to have
a single mutex_unlock and mddev_put, and use gotos where necessary.

Found-by: Jiri Slaby <jirislaby@gmail.com>
Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 18 insertions, 20 deletions

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 58bee2366ea8..65fe35b5e34a 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -3846,11 +3846,9 @@ static int md_alloc(dev_t dev, char *name)
         flush_scheduled_work();
 
         mutex_lock(&disks_mutex);
-        if (mddev->gendisk) {
-                mutex_unlock(&disks_mutex);
-                mddev_put(mddev);
-                return -EEXIST;
-        }
+        error = -EEXIST;
+        if (mddev->gendisk)
+                goto abort;
 
         if (name) {
                 /* Need to ensure that 'name' is not a duplicate.
@@ -3862,19 +3860,15 @@ static int md_alloc(dev_t dev, char *name)
                         if (mddev2->gendisk &&
                             strcmp(mddev2->gendisk->disk_name, name) == 0) {
                                 spin_unlock(&all_mddevs_lock);
-                                mutex_unlock(&disks_mutex);
-                                mddev_put(mddev);
-                                return -EEXIST;
+                                goto abort;
                         }
                 spin_unlock(&all_mddevs_lock);
         }
 
+        error = -ENOMEM;
         mddev->queue = blk_alloc_queue(GFP_KERNEL);
-        if (!mddev->queue) {
-                mutex_unlock(&disks_mutex);
-                mddev_put(mddev);
-                return -ENOMEM;
-        }
+        if (!mddev->queue)
+                goto abort;
         mddev->queue->queuedata = mddev;
 
         /* Can be unlocked because the queue is new: no concurrency */
@@ -3884,11 +3878,9 @@ static int md_alloc(dev_t dev, char *name)
 
         disk = alloc_disk(1 << shift);
         if (!disk) {
-                mutex_unlock(&disks_mutex);
                 blk_cleanup_queue(mddev->queue);
                 mddev->queue = NULL;
-                mddev_put(mddev);
-                return -ENOMEM;
+                goto abort;
         }
         disk->major = MAJOR(mddev->unit);
         disk->first_minor = unit << shift;
@@ -3910,16 +3902,22 @@ static int md_alloc(dev_t dev, char *name)
         mddev->gendisk = disk;
         error = kobject_init_and_add(&mddev->kobj, &md_ktype,
                                      &disk_to_dev(disk)->kobj, "%s", "md");
-        mutex_unlock(&disks_mutex);
-        if (error)
+        if (error) {
+                /* This isn't possible, but as kobject_init_and_add is marked
+                 * __must_check, we must do something with the result
+                 */
                 printk(KERN_WARNING "md: cannot register %s/md - name in use\n",
                        disk->disk_name);
-        else {
+                error = 0;
+        }
+ abort:
+        mutex_unlock(&disks_mutex);
+        if (!error) {
                 kobject_uevent(&mddev->kobj, KOBJ_ADD);
                 mddev->sysfs_state = sysfs_get_dirent(mddev->kobj.sd, "array_state");
         }
         mddev_put(mddev);
-        return 0;
+        return error;
 }
 
 static struct kobject *md_probe(dev_t dev, int *part, void *data)