[DTrace-devel] [PATCH 07/12] Fix drop counter handling for local-only updates

[Kris Van Hees]

On Mon, Jan 08, 2024 at 03:27:26PM -0500, Eugene Loh via DTrace-devel wrote:
> I'm not familiar with how drops are handled, but...
> Reviewed-by: Eugene Loh <eugene.loh at oracle.com>
> 
> A 2006 copyright year on a "new" file looks weird.  Maybe it's right.  I'm
> no lawyer.  Just weird.

Oops, will change.  Copied an existing test and changed it but forgot to make
sure the copyright is correct.

> On 1/5/24 00:29, Kris Van Hees via DTrace-devel wrote:
> > When at the end of a work loop, the drop counters are updates for local
> 
> "are updates"
> ->
> "are updated"

Thanks.

> > updates only (i.e. when tracing is not stopped yet), an invalid drop
> > count could be reported if a drop occured in the BEGIN probe.  The cause
> > is that the code assumed that both copies of the status data contained
> > valid data.  But when a drop occurs in the BEGIN probe, only the first
> > copy will have non-zero values.  Since local-only updates assume that
> > the two copies are identical except for a possible change due to the
> > local update, and any earlier status update would already have reported
> > any differences, it is safe to just copy all data prior to performing
> > the local updates.
> > 
> > Signed-off-by: Kris Van Hees <kris.van.hees at oracle.com>
> > ---
> >   libdtrace/dt_work.c                           |  4 ++-
> >   .../drops/drp.DTRACEDROP_DYNAMIC.local_only.d | 30 +++++++++++++++++++
> >   .../drops/drp.DTRACEDROP_DYNAMIC.local_only.r |  6 ++++
> >   3 files changed, 39 insertions(+), 1 deletion(-)
> >   create mode 100644 test/unittest/drops/drp.DTRACEDROP_DYNAMIC.local_only.d
> >   create mode 100644 test/unittest/drops/drp.DTRACEDROP_DYNAMIC.local_only.r
> > 
> > diff --git a/libdtrace/dt_work.c b/libdtrace/dt_work.c
> > index fe88a48e..6cac93ea 100644
> > --- a/libdtrace/dt_work.c
> > +++ b/libdtrace/dt_work.c
> > @@ -1,6 +1,6 @@
> >   /*
> >    * Oracle Linux DTrace.
> > - * Copyright (c) 2006, 2023, Oracle and/or its affiliates. All rights reserved.
> > + * Copyright (c) 2006, 2024, Oracle and/or its affiliates. All rights reserved.
> >    * Licensed under the Universal Permissive License v 1.0 as shown at
> >    * http://oss.oracle.com/licenses/upl.
> >    */
> > @@ -271,6 +271,8 @@ dtrace_work(dtrace_hdl_t *dtp, FILE *fp, dtrace_consume_probe_f *pfunc,
> >   	 * than once).
> >   	 */
> >   	if (!dtp->dt_stopped) {
> > +		gen = dtp->dt_statusgen;
> > +		dtp->dt_status[gen] = dtp->dt_status[gen ^ 1];
> >   		dt_add_local_status(dtp);
> >   		gen = dtp->dt_statusgen ^ 1;
> >   	} else {
> > diff --git a/test/unittest/drops/drp.DTRACEDROP_DYNAMIC.local_only.d b/test/unittest/drops/drp.DTRACEDROP_DYNAMIC.local_only.d
> > new file mode 100644
> > index 00000000..2ebcf150
> > --- /dev/null
> > +++ b/test/unittest/drops/drp.DTRACEDROP_DYNAMIC.local_only.d
> > @@ -0,0 +1,30 @@
> > +/*
> > + * Oracle Linux DTrace.
> > + * Copyright (c) 2006, 2024, Oracle and/or its affiliates. All rights reserved.
> > + * Licensed under the Universal Permissive License v 1.0 as shown at
> > + * http://oss.oracle.com/licenses/upl.
> > + */
> > +
> > +/*
> > + * Ensure that when (at the end of a work loop) a local-only update is done, we
> > + * do not end up reporting (unsigned long long)-1.
> > + *
> > + * If this bug exists, output will look like:
> > + *	dtrace: [DTRACEDROP_DYNAMIC] 1 dynamic variable drop
> > + *	dtrace: [DTRACEDROP_DYNAMIC] 18446744073709551615 dynamic variable drops
> > + */
> > +
> > +#pragma D option dynvarsize=15
> > +
> > +BEGIN
> > +{
> > +	self->a = 1;
> > +	self->b = 2;
> > +	self->c = 3;
> > +	self->d = 4;
> > +}
> > +
> > +tick-1s
> > +{
> > +	exit(0);
> > +}
> > diff --git a/test/unittest/drops/drp.DTRACEDROP_DYNAMIC.local_only.r b/test/unittest/drops/drp.DTRACEDROP_DYNAMIC.local_only.r
> > new file mode 100644
> > index 00000000..8af0a5f5
> > --- /dev/null
> > +++ b/test/unittest/drops/drp.DTRACEDROP_DYNAMIC.local_only.r
> > @@ -0,0 +1,6 @@
> > +                   FUNCTION:NAME
> > +                        :tick-1s
> > +
> > +-- @@stderr --
> > +dtrace: script 'test/unittest/drops/drp.DTRACEDROP_DYNAMIC.local_only.d' matched 2 probes
> > +dtrace: [DTRACEDROP_DYNAMIC] 1 dynamic variable drop
> 
> _______________________________________________
> DTrace-devel mailing list
> DTrace-devel at oss.oracle.com
> https://oss.oracle.com/mailman/listinfo/dtrace-devel