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>

1 files changed, 52 insertions, 42 deletions

diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
index 8f7d1237b7a0..7301cdb4b2cb 100644
--- 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;