Draft: xfs: fix off-by-one-block in xfs_discard_folio()

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2178173 Tested: With xfstests Upstream Status: https://git.kernel.org/pub/scm/fs/xfs/xfs-linux.git

Conflicts: - RHEL9 still uses xfs_discard_page()

commit 8ac5b996bf5199f15b7687ceae989f8b2a410dda Author: Dave Chinner dchinner@redhat.com Date: Sun Mar 5 15:13:23 2023 -0800

xfs: fix off-by-one-block in xfs_discard_folio()

The recent writeback corruption fixes changed the code in xfs_discard_folio() to calculate a byte range to for punching delalloc extents. A mistake was made in using round_up(pos) for the end offset, because when pos points at the first byte of a block, it does not get rounded up to point to the end byte of the block. hence the punch range is short, and this leads to unexpected behaviour in certain cases in xfs_bmap_punch_delalloc_range.

e.g. pos = 0 means we call xfs_bmap_punch_delalloc_range(0,0), so there is no previous extent and it rounds up the punch to the end of the delalloc extent it found at offset 0, not the end of the range given to xfs_bmap_punch_delalloc_range().

Fix this by handling the zero block offset case correctly.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=217030 Link: https://lore.kernel.org/linux-xfs/Y+vOfaxIWX1c%2Fyy9@bfoster/ Fixes: 7348b322332d ("xfs: xfs_bmap_punch_delalloc_range() should take a byte range") Reported-by: Pengfei Xu pengfei.xu@intel.com Found-by: Brian Foster bfoster@redhat.com Signed-off-by: Dave Chinner dchinner@redhat.com Reviewed-by: Darrick J. Wong djwong@kernel.org Signed-off-by: Darrick J. Wong djwong@kernel.org Signed-off-by: Carlos Maiolino cmaiolino@redhat.com