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From: Ingo Molnar on 21 May 2010 07:00

* Ingo Molnar <mingo(a)elte.hu> wrote:

>
> * Peter Zijlstra <peterz(a)infradead.org> wrote:
>
> > On Fri, 2010-05-21 at 12:13 +0200, Frederic Weisbecker wrote:
> > > > What exactly is the puzzlement about?
> >
> > > The fact we use the hlist API not for hlist purpose
> > > but for a list.
> >
> > I might miss the confusion, but hlist _are_ lists. Its
> > just that their structure is slightly different that
> > the regular struct list_head stuff.
>
> Using an API in such a mixed way may cause puzzlement
> ;-)

I take that back - it's clear from the function prototype
that we are using a mixed API: (hlist,list).

Sorry,

Ingo
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From: Steven Rostedt on 21 May 2010 10:10
On Fri, 2010-05-21 at 11:02 +0200, Peter Zijlstra wrote:
> plain text document attachment (perf-trace-per-cpu-fold.patch)
> Avoid the swevent hash-table by using per-tracepoint hlists.
>
> Also, avoid conditionals on the fast path by ordering with probe unregister
> so that we should never get on the callback path without the data being there.
>

> -void perf_trace_disable(int event_id)
> +void perf_trace_destroy(struct perf_event *p_event)
> {
> - struct ftrace_event_call *event;
> + struct ftrace_event_call *tp_event = p_event->tp_event;
> + int i;
>
> - mutex_lock(&event_mutex);
> - list_for_each_entry(event, &ftrace_events, list) {
> - if (event->id == event_id) {
> - perf_trace_event_disable(event);
> - module_put(event->mod);
> - break;
> + if (--tp_event->perf_refcount > 0)
> + return;
> +

You remove the event_mutex and then update the tp_event->perf_refcount
without any protection.

That tp_event->perf_refcount is global to the event not to the perf
event.

-- Steve

> + tp_event->perf_event_disable(tp_event);
> +
> + free_percpu(tp_event->perf_events);
> + tp_event->perf_events = NULL;
> +
> + if (!--total_ref_count) {
> + for (i = 0; i < 4; i++) {
> + free_percpu(perf_trace_buf[i]);
> + perf_trace_buf[i] = NULL;
> }
> }
> - mutex_unlock(&event_mutex);
> }
>


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