btrfs: backref, only collect file extent items matching backref offset

When resolving one backref of type EXTENT_DATA_REF, we collect all
references that simply reference the EXTENT_ITEM even though their
(file_pos - file_extent_item::offset) are not the same as the
btrfs_extent_data_ref::offset we are searching for.

This patch adds additional check so that we only collect references whose
(file_pos - file_extent_item::offset) == btrfs_extent_data_ref::offset.

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: ethanwu <ethanwu@synology.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
index ded46ef..f847141 100644 (file)
--- a/fs/btrfs/backref.c
+++ b/fs/btrfs/backref.c
@@ -347,33 +347,10 @@ static int add_prelim_ref(const struct btrfs_fs_info *fs_info,
                return -ENOMEM;
 
        ref->root_id = root_id;
-       if (key) {
+       if (key)
                ref->key_for_search = *key;
-               /*
-                * We can often find data backrefs with an offset that is too
-                * large (>= LLONG_MAX, maximum allowed file offset) due to
-                * underflows when subtracting a file's offset with the data
-                * offset of its corresponding extent data item. This can
-                * happen for example in the clone ioctl.
-                * So if we detect such case we set the search key's offset to
-                * zero to make sure we will find the matching file extent item
-                * at add_all_parents(), otherwise we will miss it because the
-                * offset taken form the backref is much larger then the offset
-                * of the file extent item. This can make us scan a very large
-                * number of file extent items, but at least it will not make
-                * us miss any.
-                * This is an ugly workaround for a behaviour that should have
-                * never existed, but it does and a fix for the clone ioctl
-                * would touch a lot of places, cause backwards incompatibility
-                * and would not fix the problem for extents cloned with older
-                * kernels.
-                */
-               if (ref->key_for_search.type == BTRFS_EXTENT_DATA_KEY &&
-                   ref->key_for_search.offset >= LLONG_MAX)
-                       ref->key_for_search.offset = 0;
-       } else {
+       else
                memset(&ref->key_for_search, 0, sizeof(ref->key_for_search));
-       }
 
        ref->inode_list = NULL;
        ref->level = level;
@@ -424,6 +401,7 @@ static int add_all_parents(struct btrfs_root *root, struct btrfs_path *path,
        u64 disk_byte;
        u64 wanted_disk_byte = ref->wanted_disk_byte;
        u64 count = 0;
+       u64 data_offset;
 
        if (level != 0) {
                eb = path->nodes[level];
@@ -457,11 +435,15 @@ static int add_all_parents(struct btrfs_root *root, struct btrfs_path *path,
 
                fi = btrfs_item_ptr(eb, slot, struct btrfs_file_extent_item);
                disk_byte = btrfs_file_extent_disk_bytenr(eb, fi);
+               data_offset = btrfs_file_extent_offset(eb, fi);
 
                if (disk_byte == wanted_disk_byte) {
                        eie = NULL;
                        old = NULL;
-                       count++;
+                       if (ref->key_for_search.offset == key.offset - data_offset)
+                               count++;
+                       else
+                               goto next;
                        if (extent_item_pos) {
                                ret = check_extent_in_eb(&key, eb, fi,
                                                *extent_item_pos,
@@ -513,6 +495,7 @@ static int resolve_indirect_ref(struct btrfs_fs_info *fs_info,
        int root_level;
        int level = ref->level;
        int index;
+       struct btrfs_key search_key = ref->key_for_search;
 
        root_key.objectid = ref->root_id;
        root_key.type = BTRFS_ROOT_ITEM_KEY;
@@ -545,13 +528,33 @@ static int resolve_indirect_ref(struct btrfs_fs_info *fs_info,
                goto out;
        }
 
+       /*
+        * We can often find data backrefs with an offset that is too large
+        * (>= LLONG_MAX, maximum allowed file offset) due to underflows when
+        * subtracting a file's offset with the data offset of its
+        * corresponding extent data item. This can happen for example in the
+        * clone ioctl.
+        *
+        * So if we detect such case we set the search key's offset to zero to
+        * make sure we will find the matching file extent item at
+        * add_all_parents(), otherwise we will miss it because the offset
+        * taken form the backref is much larger then the offset of the file
+        * extent item. This can make us scan a very large number of file
+        * extent items, but at least it will not make us miss any.
+        *
+        * This is an ugly workaround for a behaviour that should have never
+        * existed, but it does and a fix for the clone ioctl would touch a lot
+        * of places, cause backwards incompatibility and would not fix the
+        * problem for extents cloned with older kernels.
+        */
+       if (search_key.type == BTRFS_EXTENT_DATA_KEY &&
+           search_key.offset >= LLONG_MAX)
+               search_key.offset = 0;
        path->lowest_level = level;
        if (time_seq == SEQ_LAST)
-               ret = btrfs_search_slot(NULL, root, &ref->key_for_search, path,
-                                       0, 0);
+               ret = btrfs_search_slot(NULL, root, &search_key, path, 0, 0);
        else
-               ret = btrfs_search_old_slot(root, &ref->key_for_search, path,
-                                           time_seq);
+               ret = btrfs_search_old_slot(root, &search_key, path, time_seq);
 
        /* root node has been locked, we can release @subvol_srcu safely here */
        srcu_read_unlock(&fs_info->subvol_srcu, index);