From: BingJing Chang <bingji...@synology.com> In commit d77815461f04 ("btrfs: Avoid trucating page or punching hole in a already existed hole."), existed holes can be skipped by calling find_first_non_hole() to adjust *start and *len. However, if the given len is invalid and large, when an EXTENT_MAP_HOLE extent is found, the *len will not be set to zero because (em->start + em->len) is less than (*start + *len). Then the ret will be 1 but the *len will not be set to 0. The propagated non-zero ret will result in fallocate failure.
In the while-loop of btrfs_replace_file_extents(), len is not updated every time before it calls find_first_non_hole(). That is, after btrfs_drop_extents() successfully drops the last non-hole file extent, it may fail with -ENOSPC when attempting to drop a file extent item representing a hole. The problem can happen. After it calls find_first_non_hole(), the cur_offset will be adjusted to be larger than or equal to end. However, since the len is not set to zero. The break-loop condition (ret && !len) will not meet. After it leaves the while-loop, fallocate will return 1, which is an unexpected return value. We're not able to construct a reproducible way to let btrfs_drop_extents() fail with -ENOSPC after it drops the last non-hole file extent but with remaining holes left. However, it's quite easy to fix. We just need to update and check the len every time before we call find_first_non_hole(). To make the while loop more readable, we also pull the variable updates to the bottom of loop like this: while (cur_offset < end) { ... // update cur_offset & len // advance cur_offset & len in hole-punching case if needed } Reported-by: Robbie Ko <robbi...@synology.com> Fixes: d77815461f04 ("btrfs: Avoid trucating page or punching hole in a already existed hole.") Reviewed-by: Robbie Ko <robbi...@synology.com> Reviewed-by: Chung-Chiang Cheng <ccch...@synology.com> Signed-off-by: BingJing Chang <bingji...@synology.com> --- fs/btrfs/file.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c index 0e155f0..dccb017 100644 --- a/fs/btrfs/file.c +++ b/fs/btrfs/file.c @@ -2735,8 +2735,6 @@ int btrfs_replace_file_extents(struct inode *inode, struct btrfs_path *path, extent_info->file_offset += replace_len; } - cur_offset = drop_args.drop_end; - ret = btrfs_update_inode(trans, root, BTRFS_I(inode)); if (ret) break; @@ -2756,7 +2754,9 @@ int btrfs_replace_file_extents(struct inode *inode, struct btrfs_path *path, BUG_ON(ret); /* shouldn't happen */ trans->block_rsv = rsv; - if (!extent_info) { + cur_offset = drop_args.drop_end; + len = end - cur_offset; + if (!extent_info && len) { ret = find_first_non_hole(BTRFS_I(inode), &cur_offset, &len); if (unlikely(ret < 0)) -- 2.7.4