raid5: fix a small race condition

commit 5f9d1fde7d54a5(raid5: fix memory leak of bio integrity data)
moves bio_reset to bio_endio. But it introduces a small race condition.
It does bio_reset after raid5_release_stripe, which could make the
stripe reusable and hence reuse the bio just before bio_reset. Moving
bio_reset before raid5_release_stripe is called should fix the race.

Reported-and-tested-by: Stefan Priebe - Profihost AG <s.priebe@profihost.ag>
Signed-off-by: Shaohua Li <shli@fb.com>

drivers/md/raid5.c

@@ -2423,10 +2423,10 @@ static void raid5_end_read_request(struct bio * bi)
 		}
 	}
 	rdev_dec_pending(rdev, conf->mddev);
+	bio_reset(bi);
 	clear_bit(R5_LOCKED, &sh->dev[i].flags);
 	set_bit(STRIPE_HANDLE, &sh->state);
 	raid5_release_stripe(sh);
-	bio_reset(bi);
 }
 
 static void raid5_end_write_request(struct bio *bi)
@@ -2498,6 +2498,7 @@ static void raid5_end_write_request(struct bio *bi)
 	if (sh->batch_head && bi->bi_error && !replacement)
 		set_bit(STRIPE_BATCH_ERR, &sh->batch_head->state);
 
+	bio_reset(bi);
 	if (!test_and_clear_bit(R5_DOUBLE_LOCKED, &sh->dev[i].flags))
 		clear_bit(R5_LOCKED, &sh->dev[i].flags);
 	set_bit(STRIPE_HANDLE, &sh->state);
@@ -2505,7 +2506,6 @@ static void raid5_end_write_request(struct bio *bi)
 
 	if (sh->batch_head && sh != sh->batch_head)
 		raid5_release_stripe(sh->batch_head);
-	bio_reset(bi);
 }
 
 static void raid5_build_block(struct stripe_head *sh, int i, int previous)