Re: [PATCH 2/2] perf report: Don't add to histogram when there is no thread found

[Namhyung Kim <namhyung@kernel.org>]

On Wed, Jun 28, 2023 at 1:06 PM Namhyung Kim <namhyung@kernel.org> wrote:
>
> On Wed, Jun 28, 2023 at 3:34 AM James Clark <james.clark@arm.com> wrote:
> >
> >
> >
> > On 27/06/2023 18:19, Ian Rogers wrote:
> > > On Tue, Jun 27, 2023 at 9:58 AM Namhyung Kim <namhyung@kernel.org> wrote:
> > >>
> > >> On Tue, Jun 27, 2023 at 9:43 AM Ian Rogers <irogers@google.com> wrote:
> > >>>
> > >>> On Mon, Jun 26, 2023 at 5:02 PM Namhyung Kim <namhyung@kernel.org> wrote:
> > >>>>
> > >>>> On Mon, Jun 26, 2023 at 05:10:58PM +0100, James Clark wrote:
> > >>>>> thread__find_map() chooses to exit without assigning a thread to the
> > >>>>> addr_location in some scenarios, for example when there are samples from
> > >>>>> a guest and perf_guest == false. This results in a segfault when adding
> > >>>>> to the histogram because it uses unguarded accesses to the thread member
> > >>>>> of the addr_location.
> > >>>>
> > >>>> Looking at the commit 0dd5041c9a0ea ("perf addr_location: Add
> > >>>> init/exit/copy functions") that introduced the change, I'm not sure if
> > >>>> it's the intend behavior.
> > >>>>
> > >>>> It might change maps and map, but not thread.  Then I think no reason
> > >>>> to not set the al->thread at the beginning.
> > >>>>
> > >>>> How about this?  Ian?
> > >>>> (I guess we can get rid of the duplicate 'al->map = NULL' part)
> > >>>
> > >>> It seemed strange that we were failing to find a map (the function's
> > >>> purpose) but then populating the address_location. The change below
> > >>> brings back that somewhat odd behavior. I'm okay with reverting to the
> > >>> old behavior, clearly there were users relying on it. We should
> > >>> probably also copy maps and not just thread, as that was the previous
> > >>> behavior.
> > >>
> > >> Probably.  But it used to support samples without maps and I think
> > >> that's why it ignores the return value of thread__find_map().  So
> > >> we can expect al.map is NULL and maybe fine to leave it for now.
> > >>
> > >> As machine__resolve() returns -1 if it gets no thread, we should set
> > >> al.thread when it returns 0.
> > >>
> > >> Can I get your Acked-by?
> > >
> > > Yep:
> > > Acked-by: Ian Rogers <irogers@google.com>
> >
> > Looks good to me too. Should I resend the set with this change instead
> > of my one?
>
> No, I can take care of that.  I'll take this as your Acked-by. :)

This part is applied to perf-tools-next, thanks!