On Thu, Dec 02, 2021 at 04:29:34PM -0800, Stan Hu wrote: > A number of users have reported that under certain conditions using > the overlay filesystem, copy_file_range() can unexpectedly create a > 0-byte file. [0] > > This bug can cause significant problems because applications that copy > files expect the target file to match the source immediately after the > copy. After upgrading from Linux 5.4 to Linux 5.10, our Docker-based > CI tests started failing due to this bug, since Ruby's IO.copy_stream > uses this system call. We have worked around the problem by touching > the target file before using it, but this shouldn't be necessary. > Other projects, such as Rust, have added similar workarounds. [1] > > As discussed in the linux-fsdevel mailing list [2], the bug appears to > be present in Linux 5.6 to 5.10, but not in Linux 5.11. We should be > able to cherry-pick the following upstream patches to fix this. Could > you cherry-pick them to 5.10.x stable? I've confirmed that these > patches, applied from top to bottom to that branch, pass the > reproduction test [3]: > > 82a763e61e2b601309d696d4fa514c77d64ee1be > 9b91b6b019fda817eb52f728eb9c79b3579760bc > > The diffstat: > > fs/overlayfs/file.c | 59 > +++++++++++++++++++++++++++++++---------------------------- > 1 file changed, 31 insertions(+), 28 deletions(-) > > Note that these patches do not pick cleanly into 5.6.x - 5.9.x stable. > > [0] https://github.com/docker/for-linux/issues/1015 > [1] https://github.com/rust-lang/rust/blob/342db70ae4ecc3cd17e4fa6497f0a8d9534ccfeb/library/std/src/sys/unix/kernel_copy.rs#L565-L569 > [2] https://marc.info/?l=linux-fsdevel&m=163847383311699&w=2 > [3] https://github.com/docker/for-linux/issues/1015#issuecomment-841915668 Now queued up, thanks, greg k-h
