• Brian Foster's avatar
    mm/page-writeback.c: don't break integrity writeback on ->writepage() error · 694c20fe
    Brian Foster authored
    [ Upstream commit 3fa750dcf29e8606e3969d13d8e188cc1c0f511d ]
    
    write_cache_pages() is used in both background and integrity writeback
    scenarios by various filesystems.  Background writeback is mostly
    concerned with cleaning a certain number of dirty pages based on various
    mm heuristics.  It may not write the full set of dirty pages or wait for
    I/O to complete.  Integrity writeback is responsible for persisting a set
    of dirty pages before the writeback job completes.  For example, an
    fsync() call must perform integrity writeback to ensure data is on disk
    before the call returns.
    
    write_cache_pages() unconditionally breaks out of its processing loop in
    the event of a ->writepage() error.  This is fine for background
    writeback, which had no strict requirements and will eventually come
    around again.  This can cause problems for integrity writeback on
    filesystems that might need to clean up state associated with failed page
    writeouts.  For example, XFS performs internal delayed allocation
    accounting before returning a ->writepage() error, where applicable.  If
    the current writeback happens to be associated with an unmount and
    write_cache_pages() completes the writeback prematurely due to error, the
    filesystem is unmounted in an inconsistent state if dirty+delalloc pages
    still exist.
    
    To handle this problem, update write_cache_pages() to always process the
    full set of pages for integrity writeback regardless of ->writepage()
    errors.  Save the first encountered error and return it to the caller once
    complete.  This facilitates XFS (or any other fs that expects integrity
    writeback to process the entire set of dirty pages) to clean up its
    internal state completely in the event of persistent mapping errors.
    Background writeback continues to exit on the first error encountered.
    
    [akpm@linux-foundation.org: fix typo in comment]
    Link: http://lkml.kernel.org/r/20181116134304.32440-1-bfoster@redhat.comSigned-off-by: default avatarBrian Foster <bfoster@redhat.com>
    Reviewed-by: default avatarJan Kara <jack@suse.cz>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
    694c20fe