md/raid5: output stripe state for debug

Neil recently fixed an obscure race in break_stripe_batch_list. Debug would be
quite convenient if we know the stripe state. This is what this patch does.
Signed-off-by: NShaohua Li <shli@fb.com>

drivers/md/raid5.c

@@ -4236,7 +4236,7 @@ static void break_stripe_batch_list(struct stripe_head *head_sh,
 
 		list_del_init(&sh->batch_list);
 
-		WARN_ON_ONCE(sh->state & ((1 << STRIPE_ACTIVE) |
+		WARN_ONCE(sh->state & ((1 << STRIPE_ACTIVE) |
 					  (1 << STRIPE_SYNCING) |
 					  (1 << STRIPE_REPLACED) |
 					  (1 << STRIPE_DELAYED) |
@@ -4248,9 +4248,11 @@ static void break_stripe_batch_list(struct stripe_head *head_sh,
 					  (1 << STRIPE_DISCARD) |
 					  (1 << STRIPE_BATCH_READY) |
 					  (1 << STRIPE_BATCH_ERR) |
-					  (1 << STRIPE_BITMAP_PENDING)));
-		WARN_ON_ONCE(head_sh->state & ((1 << STRIPE_DISCARD) |
-					      (1 << STRIPE_REPLACED)));
+					  (1 << STRIPE_BITMAP_PENDING)),
+			"stripe state: %lx\n", sh->state);
+		WARN_ONCE(head_sh->state & ((1 << STRIPE_DISCARD) |
+					      (1 << STRIPE_REPLACED)),
+			"head stripe state: %lx\n", head_sh->state);
 
 		set_mask_bits(&sh->state, ~(STRIPE_EXPAND_SYNC_FLAGS |
 					    (1 << STRIPE_PREREAD_ACTIVE) |