MD: Prevent sysfs operations on uninitialized kobjects

MD: Prevent sysfs operations on uninitialized kobjects

Device-mapper does not use sysfs; but when device-mapper is leveraging
MD's RAID personalities, MD sometimes attempts to update sysfs.  This
patch adds checks for 'mddev-kobj.sd' in sysfs_[un]link_rdev to ensure
it is about to operate on something valid.  This patch also checks for
'mddev->kobj.sd' before calling 'sysfs_notify' in 'remove_and_add_spares'.
Although 'sysfs_notify' already makes this check, doing so in
'remove_and_add_spares' prevents an additional mutex operation.
Signed-off-by: Jonathan Brassow <jbrassow@redhat.com>
Signed-off-by: NeilBrown <neilb@suse.de>

drivers/md/md.c

@@ -7663,10 +7663,8 @@ static int remove_and_add_spares(struct mddev *mddev)
 				removed++;
 			}
 		}
-	if (removed)
-		sysfs_notify(&mddev->kobj, NULL,
-			     "degraded");
-
+	if (removed && mddev->kobj.sd)
+		sysfs_notify(&mddev->kobj, NULL, "degraded");
 
 	rdev_for_each(rdev, mddev) {
 		if (rdev->raid_disk >= 0 &&

drivers/md/md.h

@@ -506,7 +506,7 @@ static inline char * mdname (struct mddev * mddev)
 static inline int sysfs_link_rdev(struct mddev *mddev, struct md_rdev *rdev)
 {
 	char nm[20];
-	if (!test_bit(Replacement, &rdev->flags)) {
+	if (!test_bit(Replacement, &rdev->flags) && mddev->kobj.sd) {
 		sprintf(nm, "rd%d", rdev->raid_disk);
 		return sysfs_create_link(&mddev->kobj, &rdev->kobj, nm);
 	} else
@@ -516,7 +516,7 @@ static inline int sysfs_link_rdev(struct mddev *mddev, struct md_rdev *rdev)
 static inline void sysfs_unlink_rdev(struct mddev *mddev, struct md_rdev *rdev)
 {
 	char nm[20];
-	if (!test_bit(Replacement, &rdev->flags)) {
+	if (!test_bit(Replacement, &rdev->flags) && mddev->kobj.sd) {
 		sprintf(nm, "rd%d", rdev->raid_disk);
 		sysfs_remove_link(&mddev->kobj, nm);
 	}