Re: [PATCH 02/10] perf, trace: Use per-tracepoint-per-cpu hlist totrack events

[Peter Zijlstra]

On Fri, 2010-05-21 at 12:13 +0200, Frederic Weisbecker wrote:
> > I assumed that after probe unregister a tracepoint callback doesn't
> > happen, which then guarantees we should never get !head.

> I'm not sure about this. The tracepoints are called under rcu_read_lock(),
> but there is not synchronize_rcu() after we unregister a tracepoint, which
> means you can have a pending preempted one somewhere.
> 
> There is a call_rcu that removes the callbacks, but that only protect
> the callback themselves. 

Ah, ok, so we should do probe_unregister + synchronize_sched().

That should ensure __DO_TRACE() doesn't call into it anymore.

/me goes make a patch

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