Close race in md_probe

There is a possible race in md_probe.  If two threads call md_probe
for the same device, then one could exit (having checked that
->gendisk exists) before the other has called kobject_init_and_add,
thus returning an incomplete kobj which will cause problems when
we try to add children to it.

So extend the range of protection of disks_mutex slightly to
avoid this possibility.

Signed-off-by: Neil Brown <neilb@suse.de>

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 261322722c195c22ada84ade70fdb1669a4df487..97852099defda678291bfa24d99e38349be466bf 100644 (file)
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -3359,9 +3359,9 @@ static struct kobject *md_probe(dev_t dev, int *part, void *data)
        disk->queue = mddev->queue;
        add_disk(disk);
        mddev->gendisk = disk;
-       mutex_unlock(&disks_mutex);
        error = kobject_init_and_add(&mddev->kobj, &md_ktype, &disk->dev.kobj,
                                     "%s", "md");
+       mutex_unlock(&disks_mutex);
        if (error)
                printk(KERN_WARNING "md: cannot register %s/md - name in use\n",
                       disk->disk_name);