md/raid10: fix two bugs in handling of known-bad-blocks.

If we discover a bad block when reading we split the request and
potentially read some of it from a different device.

The code path of this has two bugs in RAID10.
1/ we get a spin_lock with _irq, but unlock without _irq!!
2/ The calculation of 'sectors_handled' is wrong, as can be clearly
   seen by comparison with raid1.c

This leads to at least 2 warnings and a probable crash is a RAID10
ever had known bad blocks.

Cc: stable@vger.kernel.org (v3.1+)
Fixes: 856e08e237
Reported-by: Damian Nowak <spam@nowaker.net>
URL: https://bugzilla.kernel.org/show_bug.cgi?id=68181
Signed-off-by: NeilBrown <neilb@suse.de>

drivers/md/raid10.c

@@ -1319,7 +1319,7 @@ read_again:
 			/* Could not read all from this device, so we will
 			 * need another r10_bio.
 			 */
-			sectors_handled = (r10_bio->sectors + max_sectors
+			sectors_handled = (r10_bio->sector + max_sectors
 					   - bio->bi_sector);
 			r10_bio->sectors = max_sectors;
 			spin_lock_irq(&conf->device_lock);
@@ -1327,7 +1327,7 @@ read_again:
 				bio->bi_phys_segments = 2;
 			else
 				bio->bi_phys_segments++;
-			spin_unlock(&conf->device_lock);
+			spin_unlock_irq(&conf->device_lock);
 			/* Cannot call generic_make_request directly
 			 * as that will be queued in __generic_make_request
 			 * and subsequent mempool_alloc might block