Re: [PATCH 01/13] perf: Simplify perf_event_alloc() error path

[Namhyung Kim]

Hi Jiri and Peter,

On Fri, Nov 3, 2023 at 5:38 AM Jiri Olsa <olsajiri@xxxxxxxxx> wrote:
>
> On Thu, Nov 02, 2023 at 04:09:20PM +0100, Peter Zijlstra wrote:
>
> SNIP
>
> > @@ -11936,24 +11957,24 @@ perf_event_alloc(struct perf_event_attr
> >        */
> >       if (pmu->task_ctx_nr == perf_invalid_context && (task || cgroup_fd != -1)) {
> >               err = -EINVAL;
> > -             goto err_pmu;
> > +             goto err;
> >       }
> >
> >       if (event->attr.aux_output &&
> >           !(pmu->capabilities & PERF_PMU_CAP_AUX_OUTPUT)) {
> >               err = -EOPNOTSUPP;
> > -             goto err_pmu;
> > +             goto err;
> >       }
> >
> >       if (cgroup_fd != -1) {
> >               err = perf_cgroup_connect(cgroup_fd, event, attr, group_leader);
> >               if (err)
> > -                     goto err_pmu;
> > +                     goto err;
> >       }
> >
> >       err = exclusive_event_init(event);
> >       if (err)
> > -             goto err_pmu;
> > +             goto err;
> >
> >       if (has_addr_filter(event)) {
> >               event->addr_filter_ranges = kcalloc(pmu->nr_addr_filters,
> > @@ -11961,7 +11982,7 @@ perf_event_alloc(struct perf_event_attr
> >                                                   GFP_KERNEL);
> >               if (!event->addr_filter_ranges) {
> >                       err = -ENOMEM;
> > -                     goto err_per_task;
> > +                     goto err;
> >               }
> >
> >               /*
> > @@ -11986,41 +12007,21 @@ perf_event_alloc(struct perf_event_attr
> >               if (event->attr.sample_type & PERF_SAMPLE_CALLCHAIN) {
> >                       err = get_callchain_buffers(attr->sample_max_stack);
> >                       if (err)
> > -                             goto err_addr_filters;
> > +                             goto err;
> >               }
> >       }
> >
> >       err = security_perf_event_alloc(event);
> >       if (err)
> > -             goto err_callchain_buffer;
> > +             goto err;
> >
> >       /* symmetric to unaccount_event() in _free_event() */
> >       account_event(event);
> >
> >       return event;
> >
> > -err_callchain_buffer:
> > -     if (!event->parent) {
> > -             if (event->attr.sample_type & PERF_SAMPLE_CALLCHAIN)
> > -                     put_callchain_buffers();
> > -     }
>
> hum, so this is now called all the time via __free_event, but it should
> be called only if we passed get_callchain_buffers call.. this could screw
> up nr_callchain_events number eventually no?

Looks like so.

>
> jirka
>
> > -err_addr_filters:
> > -     kfree(event->addr_filter_ranges);
> > -
> > -err_per_task:
> > -     exclusive_event_destroy(event);
> > -
> > -err_pmu:
> > -     if (is_cgroup_event(event))
> > -             perf_detach_cgroup(event);
> > -     if (event->destroy)
> > -             event->destroy(event);
> > -     module_put(pmu->module);

I'm afraid of this part.  If it failed at perf_init_event(), it might
call event->destroy() already.  I saw you cleared event->pmu
in the failure path.  Maybe we need the same thing for the
event->destroy.

Thanks,
Namhyung


> > -err_ns:
> > -     if (event->hw.target)
> > -             put_task_struct(event->hw.target);
> > -     call_rcu(&event->rcu_head, free_event_rcu);
> > -
> > +err:
> > +     __free_event(event);
> >       return ERR_PTR(err);
> >  }
> >
> >
> >