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

From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Brian Foster <bfoster@redhat.com>
Cc: david@fromorbit.com, linux-fsdevel@vger.kernel.org,
	vishal.l.verma@intel.com, xfs@oss.sgi.com
Subject: Re: [PATCH 19/47] xfs: add tracepoints and error injection for deferred extent freeing
Date: Tue, 2 Aug 2016 15:43:25 -0700	[thread overview]
Message-ID: <20160802224325.GN8590@birch.djwong.org> (raw)
In-Reply-To: <20160802213816.GA8100@bfoster.bfoster>

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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