md/raid5: Do not add data_offset before call to is_badblock

commit 6c0544e2 upstream.

In chunk_aligned_read() we are adding data_offset before calling
is_badblock.  But is_badblock also adds data_offset, so that is bad.

So move the addition of data_offset to after the call to
is_badblock.

This bug was introduced by commit 31c176ec
     md/raid5: avoid reading from known bad blocks.
which first appeared in 3.0.  So that patch is suitable for any
-stable kernel from 3.0.y onwards.  However it will need minor
revision for most of those (as the comment didn't appear until
recently).
Signed-off-by: majianpeng <majianpeng@gmail.com>
Signed-off-by: NeilBrown <neilb@suse.de>
[bwh: Backported to 3.2: ignored missing comment]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/md/raid5.c

@@ -3850,7 +3850,6 @@ static int chunk_aligned_read(struct mddev *mddev, struct bio * raid_bio)
 		raid_bio->bi_next = (void*)rdev;
 		align_bi->bi_bdev =  rdev->bdev;
 		align_bi->bi_flags &= ~(1 << BIO_SEG_VALID);
-		align_bi->bi_sector += rdev->data_offset;
 
 		if (!bio_fits_rdev(align_bi) ||
 		    is_badblock(rdev, align_bi->bi_sector, align_bi->bi_size>>9,
@@ -3861,6 +3860,9 @@ static int chunk_aligned_read(struct mddev *mddev, struct bio * raid_bio)
 			return 0;
 		}
 
+		/* No reshape active, so we can trust rdev->data_offset */
+		align_bi->bi_sector += rdev->data_offset;
+
 		spin_lock_irq(&conf->device_lock);
 		wait_event_lock_irq(conf->wait_for_stripe,
 				    conf->quiesce == 0,