Re: [PATCH 06/27] xfs: create helpers to record and deal with scrub problems

Darrick J. Wong
2017-09-23T07:24:08Z

On Sat, Sep 23, 2017 at 05:22:28PM +1000, Dave Chinner wrote:
> Darrick,
>
> Excuse the nasty top post, but can you wrap all this up in comments
> in the code? It all makes sense now you explain it, but I'm not
> going to remember all that in a couple of months time...

Already done.

(FWIW top-posting doesn't bother me...)

--D

>
> -Dave.
>
> On Fri, Sep 22, 2017 at 09:44:18AM -0700, Darrick J. Wong wrote:
> > On Fri, Sep 22, 2017 at 05:16:08PM +1000, Dave Chinner wrote:
> > > On Wed, Sep 20, 2017 at 05:18:14PM -0700, Darrick J. Wong wrote:
> > > > From: Darrick J. Wong <darrick.wong@oracle.com>
> > > >
> > > > Create helper functions to record crc and corruption problems, and
> > > > deal with any other runtime errors that arise.
> > > >
> > > > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> > > > ---
> > > > fs/xfs/scrub/common.c | 243 +++++++++++++++++++++++++++++++++++++++++++++++++
> > > > fs/xfs/scrub/common.h | 39 ++++++++
> > > > fs/xfs/scrub/trace.h | 193 +++++++++++++++++++++++++++++++++++++++
> > > > 3 files changed, 475 insertions(+)
> > > >
> > > >
> > > > diff --git a/fs/xfs/scrub/common.c b/fs/xfs/scrub/common.c
> > > > index 13ccb36..cf3f1365 100644
> > > > --- a/fs/xfs/scrub/common.c
> > > > +++ b/fs/xfs/scrub/common.c
> > > > @@ -47,6 +47,249 @@
> > > >
> > > > /* Common code for the metadata scrubbers. */
> > > >
> > > > +/* Check for operational errors. */
> > > > +bool
> > > > +xfs_scrub_op_ok(
> > > > + struct xfs_scrub_context *sc,
> > > > + xfs_agnumber_t agno,
> > > > + xfs_agblock_t bno,
> > > > + int *error)
> > > > +{
> > > > + switch (*error) {
> > > > + case 0:
> > > > + return true;
> > > > + case -EDEADLOCK:
> > > > + /* Used to restart an op with deadlock avoidance. */
> > > > + trace_xfs_scrub_deadlock_retry(sc->ip, sc->sm, *error);
> > > > + break;
> > > > + case -EFSBADCRC:
> > > > + case -EFSCORRUPTED:
> > > > + /* Note the badness but don't abort. */
> > > > + sc->sm->sm_flags |= XFS_SCRUB_OFLAG_CORRUPT;
> > > > + *error = 0;
> > > > + /* fall through */
> > > > + default:
> > > > + trace_xfs_scrub_op_error(sc, agno, bno, *error,
> > > > + __return_address);
> > > > + break;
> > > > + }
> > > > + return false;
> > > > +}
> > >
> > > What are the semantics here w.r.t. *error? on some errors it's
> > > cleared before we return, on others it's ignored. It's as clear as
> > > mud what we should expect from these functions...
> >
> > If there's no error, we return true to tell the caller that it's ok to
> > move on to the next check in its list.
> >
> > For non-verifier errors (e.g. ENOMEM) we return false to tell the caller
> > that there's no point in it continuing, and we preserve *error so that
> > the caller can return the *error up the stack. Checking stops
> > immediately and the error is handed to userspace.
> >
> > Verifier errors (EFSBADCRC/EFSCORRUPTED) are recorded in sm_flags and
> > the *error is cleared. We return false to tell the caller that there's
> > point in it continuing with this record. The caller returns zero to its
> > caller, which means that checking continues, having skipped whatever
> > block failed the verifier.
> >
> > > > +/* Check for metadata block optimization possibilities. */
> > > > +bool
> > > > +xfs_scrub_block_preen_ok(
> > > > + struct xfs_scrub_context *sc,
> > > > + struct xfs_buf *bp,
> > > > + bool fs_ok)
> > > > +{
> > > > + struct xfs_mount *mp = sc->mp;
> > > > + xfs_fsblock_t fsbno;
> > > > + xfs_agnumber_t agno;
> > > > + xfs_agblock_t bno;
> > > > +
> > > > + if (fs_ok)
> > > > + return fs_ok;
> > > > +
> > > > + fsbno = XFS_DADDR_TO_FSB(mp, bp->b_bn);
> > > > + agno = XFS_FSB_TO_AGNO(mp, fsbno);
> > > > + bno = XFS_FSB_TO_AGBNO(mp, fsbno);
> > > > +
> > > > + sc->sm->sm_flags |= XFS_SCRUB_OFLAG_PREEN;
> > > > + trace_xfs_scrub_block_preen(sc, agno, bno, __return_address);
> > > > + return fs_ok;
> > > > +}
> > >
> > > Again, I'm not sure what the return value semantics of the functioon
> > > are? Why does the fs_ok return shortcut exist?
> >
> > The fs_ok functions are wrappers around an if test; the results of the
> > if test are passed in as fs_ok.
> >
> > Therefore, if fs_ok then things are fine and we just skip out.
> >
> > Otherwise, we found something and we should set sm_flags and jump out.
> >
> > > Same for all the other functions...
> > >
> > > > +
> > > > +/* Check for inode metadata non-corruption problems. */
> > > > +bool
> > > > +xfs_scrub_ino_warn_ok(
> > > > + struct xfs_scrub_context *sc,
> > > > + struct xfs_buf *bp,
> > > > + bool fs_ok)
> > >
> > > Confusing. What's the difference between a corruption problem and a
> > > "non-corruption problem" that requires a warning?
> >
> > Anything that's less severe than "your fs is corrupt" but otherwise
> > requires administrator review. The inode scrubber sets this for inodes
> > with a -1 uid/gid. XFS seems fine with it, but the VFS treats -1ULL as
> > a magic "doesn't exist" value, and then userspace can't change it.
> > The quota code sets warnings if it detects quota usage exceeding the
> > hard limit, or if the limits are larger than the fs, etc.
> >
> > In these cases I'd want the administrator to have a look and/or take
> > corrective action, but XFS doesn't flag those situations as fs
> > corruption nor does xfs_repair complain about them as corruption.
> >
> > --D
> >
> > >
> > > Cheers,
> > >
> > > Dave.
> > > --
> > > Dave Chinner
> > > david@fromorbit.com
> > > --
> > > To unsubscribe from this list: send the line "unsubscribe linux-xfs" in
> > > the body of a message to majordomo@vger.kernel.org
> > > More majordomo info at http://vger.kernel.org/majordomo-info.html
> >
>
> --
> Dave Chinner
> david@fromorbit.com
> --
> To unsubscribe from this list: send the line "unsubscribe linux-xfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html