From: Filipe Manana fdmanana@suse.com
commit d4597898ba7b9d467b94a9aafd65ec408a75041f upstream.
While doing a reflink operation, if an ordered extent for a file range that does not overlap with the source and destination ranges of the reflink operation happens, we can end up having a failure in the reflink operation and return -EINVAL to user space.
The following sequence of steps explains how this can happen:
1) We have the page at file offset 315392 dirty (under delalloc);
2) A reflink operation for this file starts, using the same file as both source and destination, the source range is [372736, 409600) (length of 36864 bytes) and the destination range is [208896, 245760);
3) At btrfs_remap_file_range_prep(), we flush all delalloc in the source and destination ranges, and wait for any ordered extents in those range to complete;
4) Still at btrfs_remap_file_range_prep(), we then flush all delalloc in the inode, but we neither wait for it to complete nor any ordered extents to complete. This results in starting delalloc for the page at file offset 315392 and creating an ordered extent for that single page range;
5) We then move to btrfs_clone() and enter the loop to find file extent items to copy from the source range to destination range;
6) In the first iteration we end up at last file extent item stored in leaf A:
(...) item 131 key (143616 108 315392) itemoff 5101 itemsize 53 extent data disk bytenr 1903988736 nr 73728 extent data offset 12288 nr 61440 ram 73728
This represents the file range [315392, 376832), which overlaps with the source range to clone.
@datal is set to 61440, key.offset is 315392 and @next_key_min_offset is therefore set to 376832 (315392 + 61440).
@off (372736) is > key.offset (315392), so @new_key.offset is set to the value of @destoff (208896).
@new_key.offset == @last_dest_end (208896) so @drop_start is set to 208896 (@new_key.offset).
@datal is adjusted to 4096, as @off is > @key.offset.
So in this iteration we call btrfs_replace_file_extents() for the range [208896, 212991] (a single page, which is [@drop_start, @new_key.offset + @datal - 1]).
@last_dest_end is set to 212992 (@new_key.offset + @datal = 208896 + 4096 = 212992).
Before the next iteration of the loop, @key.offset is set to the value 376832, which is @next_key_min_offset;
7) On the second iteration btrfs_search_slot() leaves us again at leaf A, but this time pointing beyond the last slot of leaf A, as that's where a key with offset 376832 should be at if it existed. So end up calling btrfs_next_leaf();
8) btrfs_next_leaf() releases the path, but before it searches again the tree for the next key/leaf, the ordered extent for the single page range at file offset 315392 completes. That results in trimming the file extent item we processed before, adjusting its key offset from 315392 to 319488, reducing its length from 61440 to 57344 and inserting a new file extent item for that single page range, with a key offset of 315392 and a length of 4096.
Leaf A now looks like:
(...) item 132 key (143616 108 315392) itemoff 4995 itemsize 53 extent data disk bytenr 1801666560 nr 4096 extent data offset 0 nr 4096 ram 4096 item 133 key (143616 108 319488) itemoff 4942 itemsize 53 extent data disk bytenr 1903988736 nr 73728 extent data offset 16384 nr 57344 ram 73728
9) When btrfs_next_leaf() returns, it gives us a path pointing to leaf A at slot 133, since it's the first key that follows what was the last key we saw (143616 108 315392). In fact it's the same item we processed before, but its key offset was changed, so it counts as a new key;
10) So now we have:
@key.offset == 319488 @datal == 57344
@off (372736) is > key.offset (319488), so @new_key.offset is set to 208896 (@destoff value).
@new_key.offset (208896) != @last_dest_end (212992), so @drop_start is set to 212992 (@last_dest_end value).
@datal is adjusted to 4096 because @off > @key.offset.
So in this iteration we call btrfs_replace_file_extents() for the invalid range of [212992, 212991] (which is [@drop_start, @new_key.offset + @datal - 1]).
This range is empty, the end offset is smaller than the start offset so btrfs_replace_file_extents() returns -EINVAL, which we end up returning to user space and fail the reflink operation.
This all happens because the range of this file extent item was already processed in the previous iteration.
This scenario can be triggered very sporadically by fsx from fstests, for example with test case generic/522.
So fix this by having btrfs_clone() skip file extent items that cover a file range that we have already processed.
CC: stable@vger.kernel.org # 5.10+ Reviewed-by: Boris Burkov boris@bur.io Signed-off-by: Filipe Manana fdmanana@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/btrfs/reflink.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-)
--- a/fs/btrfs/reflink.c +++ b/fs/btrfs/reflink.c @@ -344,6 +344,7 @@ static int btrfs_clone(struct inode *src int ret; const u64 len = olen_aligned; u64 last_dest_end = destoff; + u64 prev_extent_end = off;
ret = -ENOMEM; buf = kvmalloc(fs_info->nodesize, GFP_KERNEL); @@ -363,7 +364,6 @@ static int btrfs_clone(struct inode *src key.offset = off;
while (1) { - u64 next_key_min_offset = key.offset + 1; struct btrfs_file_extent_item *extent; u64 extent_gen; int type; @@ -431,14 +431,21 @@ process_slot: * The first search might have left us at an extent item that * ends before our target range's start, can happen if we have * holes and NO_HOLES feature enabled. + * + * Subsequent searches may leave us on a file range we have + * processed before - this happens due to a race with ordered + * extent completion for a file range that is outside our source + * range, but that range was part of a file extent item that + * also covered a leading part of our source range. */ - if (key.offset + datal <= off) { + if (key.offset + datal <= prev_extent_end) { path->slots[0]++; goto process_slot; } else if (key.offset >= off + len) { break; } - next_key_min_offset = key.offset + datal; + + prev_extent_end = key.offset + datal; size = btrfs_item_size(leaf, slot); read_extent_buffer(leaf, buf, btrfs_item_ptr_offset(leaf, slot), size); @@ -550,7 +557,7 @@ process_slot: break;
btrfs_release_path(path); - key.offset = next_key_min_offset; + key.offset = prev_extent_end;
if (fatal_signal_pending(current)) { ret = -EINTR;