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From: Frederic Weisbecker on 10 Jun 2010 12:40
On Thu, Jun 10, 2010 at 12:50:17PM +0200, Peter Zijlstra wrote:
> On Thu, 2010-06-10 at 05:49 +0200, Frederic Weisbecker wrote:
> > If we call perf_event_stop() on a software event and then the
> > disable() pmu callback on them after that, we'll call twice
> > hlist_del_rcu() on the same hlist node and then bring a crash
> > by dereferencing LIST_POISON2.
> >
> > Just use hlist_del_init_rcu() instead to fix this problem.
> >
> > This preparates for new context exclusions.
> >
> > Signed-off-by: Frederic Weisbecker <fweisbec(a)gmail.com>
> > Cc: Ingo Molnar <mingo(a)elte.hu>
> > Cc: Peter Zijlstra <a.p.zijlstra(a)chello.nl>
> > Cc: Arnaldo Carvalho de Melo <acme(a)redhat.com>
> > Cc: Paul Mackerras <paulus(a)samba.org>
> > Cc: Stephane Eranian <eranian(a)google.com>
> > Cc: Cyrill Gorcunov <gorcunov(a)gmail.com>
> > Cc: Zhang Yanmin <yanmin_zhang(a)linux.intel.com>
> > Cc: Steven Rostedt <rostedt(a)goodmis.org>
> > ---
> > kernel/perf_event.c | 2 +-
> > kernel/trace/trace_event_perf.c | 2 +-
> > 2 files changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/perf_event.c b/kernel/perf_event.c
> > index 5c004f7..2d818bc 100644
> > --- a/kernel/perf_event.c
> > +++ b/kernel/perf_event.c
> > @@ -4291,7 +4291,7 @@ static int perf_swevent_enable(struct perf_event *event)
> >
> > static void perf_swevent_disable(struct perf_event *event)
> > {
> > - hlist_del_rcu(&event->hlist_entry);
> > + hlist_del_init_rcu(&event->hlist_entry);
> > }
> >
> > static void perf_swevent_void(struct perf_event *event)
> > diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
> > index 4799d70..7bc1f26 100644
> > --- a/kernel/trace/trace_event_perf.c
> > +++ b/kernel/trace/trace_event_perf.c
> > @@ -122,7 +122,7 @@ int perf_trace_enable(struct perf_event *p_event)
> >
> > void perf_trace_disable(struct perf_event *p_event)
> > {
> > - hlist_del_rcu(&p_event->hlist_entry);
> > + hlist_del_init_rcu(&p_event->hlist_entry);
> > }
> >
> > void perf_trace_destroy(struct perf_event *p_event)
>
>
> Ok, so then why did you need the first patch?


Because we need perf_event_stop/start to act on software events too.
The perf_event_enable,stop/start,perf_event_disable avoidance for
software is more an optimization that could be thought in another
patchset though.

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