md: raid10: fix use-after-free of bio

In case of read errors raid10d tries to print a nice error message,
unfortunately using data from an already put bio.

Signed-off-by: Maik Hampel <m.hampel@gmx.de>
Acked-By: NeilBrown <neilb@suse.de>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/md/raid10.c

@@ -1557,16 +1557,17 @@ static void raid10d(mddev_t *mddev)
 			bio = r10_bio->devs[r10_bio->read_slot].bio;
 			r10_bio->devs[r10_bio->read_slot].bio =
 				mddev->ro ? IO_BLOCKED : NULL;
-			bio_put(bio);
 			mirror = read_balance(conf, r10_bio);
 			if (mirror == -1) {
 				printk(KERN_ALERT "raid10: %s: unrecoverable I/O"
 				       " read error for block %llu\n",
 				       bdevname(bio->bi_bdev,b),
 				       (unsigned long long)r10_bio->sector);
 				raid_end_bio_io(r10_bio);
+				bio_put(bio);
 			} else {
 				const int do_sync = bio_sync(r10_bio->master_bio);
+				bio_put(bio);
 				rdev = conf->mirrors[mirror].rdev;
 				if (printk_ratelimit())
 					printk(KERN_ERR "raid10: %s: redirecting sector %llu to"