bcache: Fix a journalling reclaim after recovery bug

On recovery we weren't correctly keeping track of what journal buckets had open
journal entries, thus it was possible for them to be overwritten until we'd
written all new journal entries.

Signed-off-by: Kent Overstreet <kmo@daterainc.com>

drivers/md/bcache/journal.c

@@ -237,8 +237,14 @@ int bch_journal_read(struct cache_set *c, struct list_head *list)
 		for (i = 0; i < ca->sb.njournal_buckets; i++)
 			if (ja->seq[i] > seq) {
 				seq = ja->seq[i];
-				ja->cur_idx = ja->discard_idx =
-					ja->last_idx = i;
+				/*
+				 * When journal_reclaim() goes to allocate for
+				 * the first time, it'll use the bucket after
+				 * ja->cur_idx
+				 */
+				ja->cur_idx = i;
+				ja->last_idx = ja->discard_idx = (i + 1) %
+					ca->sb.njournal_buckets;
 
 			}
 	}