On Thu, Mar 25, 2021 at 09:56:22AM +0800, bingjingc wrote: > 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>
Thanks, added to misc-next.