On Mon, Jun 22, 2020 at 04:28:43PM -0700, Darrick J. Wong wrote:
> On Tue, Jun 23, 2020 at 08:08:39AM +1000, Dave Chinner wrote:
> > On Mon, Jun 22, 2020 at 10:17:13AM -0700, Darrick J. Wong wrote:
> > > From: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> > >
> > > The data fork scrubber calls filemap_write_and_wait to flush dirty pages
> > > and delalloc reservations out to disk prior to checking the data fork's
> > > extent mappings. Unfortunately, this means that scrub can consume the
> > > EIO/ENOSPC errors that would otherwise have stayed around in the address
> > > space until (we hope) the writer application calls fsync to persist data
> > > and collect errors. The end result is that programs that wrote to a
> > > file might never see the error code and proceed as if nothing were
> > > wrong.
> > >
> > > xfs_scrub is not in a position to notify file writers about the
> > > writeback failure, and it's only here to check metadata, not file
> > > contents. Therefore, if writeback fails, we should stuff the error code
> > > back into the address space so that an fsync by the writer application
> > > can pick that up.
> > >
> > > Fixes: 99d9d8d05da2 ("xfs: scrub inode block mappings")
> > > Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> > > ---
> > > fs/xfs/scrub/bmap.c | 10 +++++++++-
> > > 1 file changed, 9 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/fs/xfs/scrub/bmap.c b/fs/xfs/scrub/bmap.c
> > > index 7badd6dfe544..03be7cf3fe5a 100644
> > > --- a/fs/xfs/scrub/bmap.c
> > > +++ b/fs/xfs/scrub/bmap.c
> > > @@ -47,7 +47,15 @@ xchk_setup_inode_bmap(
> > > sc->sm->sm_type == XFS_SCRUB_TYPE_BMBTD) {
> > > inode_dio_wait(VFS_I(sc->ip));
> > > error = filemap_write_and_wait(VFS_I(sc->ip)->i_mapping);
> > > - if (error)
> > > + if (error == -ENOSPC || error == -EIO) {
> > > + /*
> > > + * If writeback hits EIO or ENOSPC, reflect it back
> > > + * into the address space mapping so that a writer
> > > + * program calling fsync to look for errors will still
> > > + * capture the error.
> > > + */
> > > + mapping_set_error(VFS_I(sc->ip)->i_mapping, error);
> > > + } else if (error)
> > > goto out;
> >
> > calling mapping_set_error() seems reasonable here and you've
> > explained that well, but shouldn't the error then be processed the
> > same way as all other errors? i.e. by jumping to out?
> >
> > If we are now continuing to scrub the bmap after ENOSPC/EIO occur,
> > why?
>
> Heh, ok, more explanation is needed. How about this?
>
> /*
> * If writeback hits EIO or ENOSPC, reflect it back into the
> * address space mapping so that a writer program calling fsync
> * to look for errors will still capture the error.
> *
> * However, we continue into the extent mapping checks because
> * write failures do not necessarily imply anything about the
> * correctness of the file metadata. The metadata and the file
> * data could be on completely separate devices; a media failure
> * might only affect a subset of the disk, etc.
> */
Ok. Does scrub deal with left-over delalloc extents correctly in
this case?
Cheers,
--
Dave Chinner
david@xxxxxxxxxxxxx
