On Sat, Oct 19, 2024 at 09:16:01AM -0700, Darrick J. Wong wrote:
> On Fri, Oct 18, 2024 at 12:28:37PM -0400, Theodore Ts'o wrote:
> > I've been running a watcher which automatically kicks off xfstests on
> > some 20+ file system configurations for btrfs, ext4, f2fs, and
> > xfstests every time fs-next gets updated, and I've noticed that
> > generic/564 has been failing essentially for all of the configurations
> > that I test. The test succeeds on rc3; it's only failing on fs-next,
> > so it's something in Linux next.
> >
> > The weird thing is when I attempted to bisect it (and I've tried twice
> > in the last two days) the bisection identifies the first bad commit as
> > Stephen's merge of vfs-branuer into linux-next:
> >
> > commit b3efa2373eed4e08e62b50898f8c3a4e757e14c3 (linux-next/fs-next)
> > Merge: 233650c5fbb8 2232c1874e5c
> > Author: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
> > Date: Thu Oct 17 12:45:50 2024 +1100
> >
> > next-20241016/vfs-brauner
> >
> > # Conflicts:
> > # fs/btrfs/file.c
> > # include/linux/iomap.h
> >
> > The merge resolution looks utterly innocuous, it seems unrelated to
> > what generic/564 tests, which is the errors returned by copy_file_range(2):
> >
> > # Exercise copy_file_range() syscall error conditions.
> > #
> > # This is a regression test for kernel commit:
> > # 96e6e8f4a68d ("vfs: add missing checks to copy_file_range")
> > #
> >
> >
> > # diff -u /root/xfstests/tests/generic/564.out /results/ext4/results-4k/generic/564.out.bad
> > --- /root/xfstests/tests/generic/564.out 2024-10-15 13:27:36.000000000
> > -0400
> > +++ /results/ext4/results-4k/generic/564.out.bad 2024-10-18 12:23:58.62
> > 9855983 -0400
> > @@ -29,9 +29,10 @@
> > copy_range: Value too large for defined data type
> >
> > source range beyond 8TiB returns 0
> > +copy_range: Value too large for defined data type
> >
> > destination range beyond 8TiB returns EFBIG
> > -copy_range: File too large
> > +copy_range: Value too large for defined data type
> >
> > destination larger than rlimit returns EFBIG
> > File size limit exceeded
> >
> >
> > Could someone take a look, and let me know if I've missed something
> > obvious?
>
> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/fs/read_write.c?h=fs-next&id=0f0f217df68fd72d91d2de6e85a6dd80fa1f5c95
> perhaps?
>
> I think the problem here is that in the old code:
>
> pos_in + count < pos_in
>
> @count is unsigned, so I think the compiler uses an unsigned comparison
> and thus pos_in + count is a very large positive value, instead of the
> negative value that the code author (who could possibly be me :P)
> thought they were getting. Hence this now triggers EOVERFLOW instead of
> the "Shorten the copy to EOF" or generic_write_check_limits EFBIG logic.
>
> To Mr. Sun: did you see these regressions when you tested this patch?
So we should drop this patch for now.
