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>

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 58bee23..65fe35b 100644 (file)
--- 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)