Re: [PATCH 19/47] xfs: add tracepoints and error injection for deferred extent freeing

Darrick J. Wong
2016-08-02T22:43:37Z

On Tue, Aug 02, 2016 at 05:38:17PM -0400, Brian Foster wrote:
> On Tue, Aug 02, 2016 at 01:24:25PM -0700, Darrick J. Wong wrote:
> > On Tue, Aug 02, 2016 at 02:48:00PM -0400, Brian Foster wrote:
> > > On Wed, Jul 20, 2016 at 09:58:10PM -0700, Darrick J. Wong wrote:
> > > > Add a couple of tracepoints for the deferred extent free operation and
> > > > a site for injecting errors while finishing the operation. This makes
> > > > it easier to debug deferred ops and test log redo.
> > > >
> > > > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> > > > ---
> > > > fs/xfs/libxfs/xfs_alloc.c | 7 +++++++
> > > > fs/xfs/libxfs/xfs_bmap.c | 2 ++
> > > > fs/xfs/xfs_error.h | 4 +++-
> > > > fs/xfs/xfs_trace.h | 5 ++++-
> > > > 4 files changed, 16 insertions(+), 2 deletions(-)
> > > >
> > > >
> > > > diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
> > > > index 5993f87..22ac3f1 100644
> > > > --- a/fs/xfs/libxfs/xfs_alloc.c
> > > > +++ b/fs/xfs/libxfs/xfs_alloc.c
> > > > @@ -2702,6 +2702,13 @@ xfs_free_extent(
> > > >
> > > > ASSERT(len != 0);
> > > >
> > > > + trace_xfs_bmap_free_deferred(mp, agno, 0, agbno, len);
> > > > +
> > >
> > > Hmm, but the bmap code isn't the only caller here. I was thinking that
> > > maybe we'd be better served by pushing these down into xfs_defer_add()
> > > and friends, but I guess we don't necessarily have the extent
> > > information at that layer.
> >
> > Correct, we don't.
> >
> > > How about we just rename these tracepoints to match the function names
> > > so they don't confuse me in the future? :)
> >
> > I broke with the function name convention so that the entry and exit
> > tracepoints to deferred items would all have names that easily matched
> > wildcards to make my life easier:
> >
> > # trace-cmd record -e 'xfs_*_defer' -e 'xfs_*_deferred' -F ...
> >
>
> The xfs_bmap_free_defer tp seems reasonable, but xfs_bmap_free_deferred
> doesn't really make sense when called via other places where nothing has
> been deferred.
>
> I'm not totally sure I follow what the goal is with this tracepoint wrt
> to naming that the trace_xfs_defer_*() tracepoints don't already achieve
> (combined with standard infrastructure tracepoints), but if the name is
> important, we should at least put it somewhere where it's only triggered
> via a deferred operation (e.g., xfs_extent_free_finish_item()).

Crap, you're right, the tp is in the wrong place. xfs_trans_free_extent() it
is. Might as well rename them to xfs_extent_free_defer* while I'm at it.

--D

>
> > > > + if (XFS_TEST_ERROR(false, mp,
> > > > + XFS_ERRTAG_FREE_EXTENT,
> > > > + XFS_RANDOM_FREE_EXTENT))
> > > > + return -EIO;
> > > > +
> > > > error = xfs_free_extent_fix_freelist(tp, agno, &agbp);
> > > > if (error)
> > > > return error;
> > > > diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
> > > > index 540a6b7..8e14ff4 100644
> > > > --- a/fs/xfs/libxfs/xfs_bmap.c
> > > > +++ b/fs/xfs/libxfs/xfs_bmap.c
> > > > @@ -596,6 +596,8 @@ xfs_bmap_add_free(
> > > > new = kmem_zone_alloc(xfs_bmap_free_item_zone, KM_SLEEP);
> > > > new->xefi_startblock = bno;
> > > > new->xefi_blockcount = (xfs_extlen_t)len;
> > > > + trace_xfs_bmap_free_defer(mp, XFS_FSB_TO_AGNO(mp, bno), 0,
> > > > + XFS_FSB_TO_AGBNO(mp, bno), len);
> > > > xfs_defer_add(dfops, XFS_DEFER_OPS_TYPE_FREE, &new->xefi_list);
> > > > }
> > > >
> > > > diff --git a/fs/xfs/xfs_error.h b/fs/xfs/xfs_error.h
> > > > index 2e4f67f..da6f951 100644
> > > > --- a/fs/xfs/xfs_error.h
> > > > +++ b/fs/xfs/xfs_error.h
> > > > @@ -90,7 +90,8 @@ extern void xfs_verifier_error(struct xfs_buf *bp);
> > > > #define XFS_ERRTAG_STRATCMPL_IOERR 19
> > > > #define XFS_ERRTAG_DIOWRITE_IOERR 20
> > > > #define XFS_ERRTAG_BMAPIFORMAT 21
> > > > -#define XFS_ERRTAG_MAX 22
> > > > +#define XFS_ERRTAG_FREE_EXTENT 22
> > > > +#define XFS_ERRTAG_MAX 23
> > > >
> > > > /*
> > > > * Random factors for above tags, 1 means always, 2 means 1/2 time, etc.
> > > > @@ -117,6 +118,7 @@ extern void xfs_verifier_error(struct xfs_buf *bp);
> > > > #define XFS_RANDOM_STRATCMPL_IOERR (XFS_RANDOM_DEFAULT/10)
> > > > #define XFS_RANDOM_DIOWRITE_IOERR (XFS_RANDOM_DEFAULT/10)
> > > > #define XFS_RANDOM_BMAPIFORMAT XFS_RANDOM_DEFAULT
> > > > +#define XFS_RANDOM_FREE_EXTENT 1
> > > >
> > >
> > > Why not XFS_RANDOM_DEFAULT?
> >
> > I don't want the injected redo errors going off at random -- I want to set
> > one and have it go off the very next time we hit it. This way I can write
> > the xfstests like so:
> >
> > mkfs/mount
> > write to a file; sync
> > set a logic bomb for the next time we free an extent
> > truncate the file
> > <watch bomb go off>
> > unmount
> > check that xfs_repair grumbles about the dirty log
> > mount
> > check the file
> >
> > Were the free-extent bomb set to go off at XFS_RANDOM_DEFAULT intervals, it'd
> > only have a 1/100 chance of triggering, which makes it harder to test.
> >
>
> Ok.
>
> Brian
>
> > --D
> >
> > >
> > > Brian
> > >
> > > > #ifdef DEBUG
> > > > extern int xfs_error_test_active;
> > > > diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h
> > > > index a45b030..939caf5 100644
> > > > --- a/fs/xfs/xfs_trace.h
> > > > +++ b/fs/xfs/xfs_trace.h
> > > > @@ -2417,9 +2417,12 @@ DEFINE_DEFER_PENDING_EVENT(xfs_defer_pending_cancel);
> > > > DEFINE_DEFER_PENDING_EVENT(xfs_defer_pending_finish);
> > > > DEFINE_DEFER_PENDING_EVENT(xfs_defer_pending_abort);
> > > >
> > > > -DEFINE_PHYS_EXTENT_DEFERRED_EVENT(xfs_defer_phys_extent);
> > > > DEFINE_MAP_EXTENT_DEFERRED_EVENT(xfs_defer_map_extent);
> > > >
> > > > +#define DEFINE_BMAP_FREE_DEFERRED_EVENT DEFINE_PHYS_EXTENT_DEFERRED_EVENT
> > > > +DEFINE_BMAP_FREE_DEFERRED_EVENT(xfs_bmap_free_defer);
> > > > +DEFINE_BMAP_FREE_DEFERRED_EVENT(xfs_bmap_free_deferred);
> > > > +
> > > > #endif /* _TRACE_XFS_H */
> > > >
> > > > #undef TRACE_INCLUDE_PATH
> > > >
> > > > _______________________________________________
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> > > > xfs@oss.sgi.com
> > > > http://oss.sgi.com/mailman/listinfo/xfs