Re: [PATCH v5 1/5] perf sched: Add missing mmap2 handler in timehist

[Ian Rogers]

On Wed, May 6, 2026 at 6:22 AM Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> wrote:
>
> On Tue, May 05, 2026 at 05:45:42PM -0700, Ian Rogers wrote:
> > perf_sched__timehist() registers event handlers for options using the
> > sched->tool struct. It registers handlers for MMAP, COMM, EXIT, FORK, etc.
> > but completely omits registering a handler for MMAP2 events.
> >
> > Failing to register both MMAP and MMAP2 handlers causes modern systems
> > (which primarily output MMAP2 records) to silently drop VMA map mappings.
> > This results in uninitialized machine/thread mapping structures, making it
> > impossible to resolve shared library instruction pointers (IPs) to dynamic
> > symbols/DSOs during timehist callchain analysis.
> >
> > Fix this by correctly registering perf_event__process_mmap2 in
> > sched->tool inside perf_sched__timehist().
> >
> > Assisted-by: Gemini-CLI:Google Gemini 3
> > Fixes: 5bbfec0ad93c ("perf sched: Implement timehist option")
>
> I'm picking patches 1 and 2 as they're simple and passed sashiko review,
> but:
>
> ⬢ [acme@toolbx perf-tools-next2]$ git show 5bbfec0ad93c
> fatal: ambiguous argument '5bbfec0ad93c': unknown revision or path not in the working tree.
> Use '--' to separate paths from revisions, like this:
> 'git <command> [<revision>...] -- [<file>...]'
> ⬢ [acme@toolbx perf-tools-next2]$
>
> The right one is:
>
> Fixes: 49394a2a24c78ce0 ("perf sched timehist: Introduce timehist command")
>
> I checked and at the time, mmap2 was already present and it missed
> adding this handler.
>
> I fixed it, in case I'm missing something, lemme know,

Sounds good. I reworked patch3 because the remove/insert pattern was
potentially racy. Now, with the write lock held it mutates the map
entry in place and then marks the backing maps as being unsorted.
Sashiko reviews made me aware of about four instances of this
potential bug. I've also tweaked the ASLR code to make it more robust
against colliding host/guest VM PIDs. I'm running sashiko locally and
will post the next version when satisfied. For some reason the
external Sashiko seems to be catching different issues :-/

Thanks,
Ian

> - Arnaldo
>
> > Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
> > ---
> >  tools/perf/builtin-sched.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
> > index 555247568e7a..241c2f808f7b 100644
> > --- a/tools/perf/builtin-sched.c
> > +++ b/tools/perf/builtin-sched.c
> > @@ -3299,6 +3299,7 @@ static int perf_sched__timehist(struct perf_sched *sched)
> >        */
> >       sched->tool.sample       = perf_timehist__process_sample;
> >       sched->tool.mmap         = perf_event__process_mmap;
> > +     sched->tool.mmap2        = perf_event__process_mmap2;
> >       sched->tool.comm         = perf_event__process_comm;
> >       sched->tool.exit         = perf_event__process_exit;
> >       sched->tool.fork         = perf_event__process_fork;
> > --
> > 2.54.0.545.g6539524ca2-goog