Btrfs: fix tree mod log for root replacements at leaf level
authorJan Schmidt <list.btrfs@jan-o-sch.net>
Thu, 21 Jun 2012 08:59:13 +0000 (10:59 +0200)
committerJan Schmidt <list.btrfs@jan-o-sch.net>
Wed, 27 Jun 2012 14:34:38 +0000 (16:34 +0200)
For the tree mod log, we don't log any operations at leaf level. If the root
is at the leaf level (i.e. the tree consists only of the root), then
__tree_mod_log_oldest_root will find a ROOT_REPLACE operation in the log
(because we always log that one no matter which level), but no other
operations.

With this patch __tree_mod_log_oldest_root exits cleanly instead of
BUGging in this situation. get_old_root checks if its really a root at leaf
level in case we don't have any operations and WARNs if this assumption
breaks.

Signed-off-by: Jan Schmidt <list.btrfs@jan-o-sch.net>
fs/btrfs/ctree.c

index 15cbc2bf4ff0ed11f8bb2e163bc1960c65b27fa7..7d1e4fc5fb6ad772b750282b285b19fa74393367 100644 (file)
@@ -1024,11 +1024,18 @@ __tree_mod_log_oldest_root(struct btrfs_fs_info *fs_info,
                if (!looped && !tm)
                        return 0;
                /*
-                * we must have key remove operations in the log before the
-                * replace operation.
+                * if there are no tree operation for the oldest root, we simply
+                * return it. this should only happen if that (old) root is at
+                * level 0.
                 */
-               BUG_ON(!tm);
+               if (!tm)
+                       break;
 
+               /*
+                * if there's an operation that's not a root replacement, we
+                * found the oldest version of our root. normally, we'll find a
+                * MOD_LOG_KEY_REMOVE_WHILE_FREEING operation here.
+                */
                if (tm->op != MOD_LOG_ROOT_REPLACE)
                        break;
 
@@ -1192,16 +1199,8 @@ get_old_root(struct btrfs_root *root, u64 time_seq)
        }
 
        tm = tree_mod_log_search(root->fs_info, logical, time_seq);
-       /*
-        * there was an item in the log when __tree_mod_log_oldest_root
-        * returned. this one must not go away, because the time_seq passed to
-        * us must be blocking its removal.
-        */
-       BUG_ON(!tm);
-
        if (old_root)
-               eb = alloc_dummy_extent_buffer(tm->index << PAGE_CACHE_SHIFT,
-                                              root->nodesize);
+               eb = alloc_dummy_extent_buffer(logical, root->nodesize);
        else
                eb = btrfs_clone_extent_buffer(root->node);
        btrfs_tree_read_unlock(root->node);
@@ -1216,7 +1215,10 @@ get_old_root(struct btrfs_root *root, u64 time_seq)
                btrfs_set_header_level(eb, old_root->level);
                btrfs_set_header_generation(eb, old_generation);
        }
-       __tree_mod_log_rewind(eb, time_seq, tm);
+       if (tm)
+               __tree_mod_log_rewind(eb, time_seq, tm);
+       else
+               WARN_ON(btrfs_header_level(eb) != 0);
        extent_buffer_get(eb);
 
        return eb;