Btrfs: don't assume to be on the correct extent in add_all_parents

add_all_parents did assume that path is already at a correct extent data
item, which may not be true in case of data extents that were partly
rewritten and splitted.

We need to check if we're on a matching extent for every item and only
for the ones after the first. The loop is changed to do this now.

This patch also fixes a bug introduced with commit 3b127fd8 "Btrfs:
remove obsolete btrfs_next_leaf call from __resolve_indirect_ref".
The removal of next_leaf did sometimes result in slot==nritems when
the above described case happens, and thus resulting in invalid values
(e.g. wanted_obejctid) in add_all_parents (leading to missed backrefs
or even crashes).

Signed-off-by: Alexander Block <ablock84@googlemail.com>
Signed-off-by: Jan Schmidt <list.btrfs@jan-o-sch.net>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
index 8f7d123..7301cdb 100644 (file)
--- a/fs/btrfs/backref.c
+++ b/fs/btrfs/backref.c
@@ -179,61 +179,74 @@ static int __add_prelim_ref(struct list_head *head, u64 root_id,
 
 static int add_all_parents(struct btrfs_root *root, struct btrfs_path *path,
                                struct ulist *parents, int level,
-                               struct btrfs_key *key, u64 time_seq,
+                               struct btrfs_key *key_for_search, u64 time_seq,
                                u64 wanted_disk_byte,
                                const u64 *extent_item_pos)
 {
-       int ret;
-       int slot = path->slots[level];
-       struct extent_buffer *eb = path->nodes[level];
+       int ret = 0;
+       int slot;
+       struct extent_buffer *eb;
+       struct btrfs_key key;
        struct btrfs_file_extent_item *fi;
        struct extent_inode_elem *eie = NULL;
        u64 disk_byte;
-       u64 wanted_objectid = key->objectid;
 
-add_parent:
-       if (level == 0 && extent_item_pos) {
-               fi = btrfs_item_ptr(eb, slot, struct btrfs_file_extent_item);
-               ret = check_extent_in_eb(key, eb, fi, *extent_item_pos, &eie);
+       if (level != 0) {
+               eb = path->nodes[level];
+               ret = ulist_add(parents, eb->start, 0, GFP_NOFS);
                if (ret < 0)
                        return ret;
-       }
-       ret = ulist_add(parents, eb->start, (unsigned long)eie, GFP_NOFS);
-       if (ret < 0)
-               return ret;
-
-       if (level != 0)
                return 0;
+       }
 
        /*
-        * if the current leaf is full with EXTENT_DATA items, we must
-        * check the next one if that holds a reference as well.
-        * ref->count cannot be used to skip this check.
-        * repeat this until we don't find any additional EXTENT_DATA items.
+        * We normally enter this function with the path already pointing to
+        * the first item to check. But sometimes, we may enter it with
+        * slot==nritems. In that case, go to the next leaf before we continue.
         */
-       while (1) {
-               eie = NULL;
+       if (path->slots[0] >= btrfs_header_nritems(path->nodes[0]))
                ret = btrfs_next_old_leaf(root, path, time_seq);
-               if (ret < 0)
-                       return ret;
-               if (ret)
-                       return 0;
 
+       while (!ret) {
                eb = path->nodes[0];
-               for (slot = 0; slot < btrfs_header_nritems(eb); ++slot) {
-                       btrfs_item_key_to_cpu(eb, key, slot);
-                       if (key->objectid != wanted_objectid ||
-                           key->type != BTRFS_EXTENT_DATA_KEY)
-                               return 0;
-                       fi = btrfs_item_ptr(eb, slot,
-                                               struct btrfs_file_extent_item);
-                       disk_byte = btrfs_file_extent_disk_bytenr(eb, fi);
-                       if (disk_byte == wanted_disk_byte)
-                               goto add_parent;
+               slot = path->slots[0];
+
+               btrfs_item_key_to_cpu(eb, &key, slot);
+
+               if (key.objectid != key_for_search->objectid ||
+                   key.type != BTRFS_EXTENT_DATA_KEY)
+                       break;
+
+               fi = btrfs_item_ptr(eb, slot, struct btrfs_file_extent_item);
+               disk_byte = btrfs_file_extent_disk_bytenr(eb, fi);
+
+               if (disk_byte == wanted_disk_byte) {
+                       eie = NULL;
+                       if (extent_item_pos) {
+                               ret = check_extent_in_eb(&key, eb, fi,
+                                               *extent_item_pos,
+                                               &eie);
+                               if (ret < 0)
+                                       break;
+                       }
+                       if (!ret) {
+                               ret = ulist_add(parents, eb->start,
+                                               (unsigned long)eie, GFP_NOFS);
+                               if (ret < 0)
+                                       break;
+                               if (!extent_item_pos) {
+                                       ret = btrfs_next_old_leaf(root, path,
+                                                       time_seq);
+                                       continue;
+                               }
+                       }
                }
+               ret = btrfs_next_old_item(root, path, time_seq);
        }
 
-       return 0;
+       if (ret > 0)
+               ret = 0;
+       return ret;
 }
 
 /*
@@ -250,7 +263,6 @@ static int __resolve_indirect_ref(struct btrfs_fs_info *fs_info,
        struct btrfs_path *path;
        struct btrfs_root *root;
        struct btrfs_key root_key;
-       struct btrfs_key key = {0};
        struct extent_buffer *eb;
        int ret = 0;
        int root_level;
@@ -295,11 +307,9 @@ static int __resolve_indirect_ref(struct btrfs_fs_info *fs_info,
                goto out;
        }
 
-       if (level == 0)
-               btrfs_item_key_to_cpu(eb, &key, path->slots[0]);
-
-       ret = add_all_parents(root, path, parents, level, &key, time_seq,
-                               ref->wanted_disk_byte, extent_item_pos);
+       ret = add_all_parents(root, path, parents, level, &ref->key_for_search,
+                               time_seq, ref->wanted_disk_byte,
+                               extent_item_pos);
 out:
        btrfs_free_path(path);
        return ret;