Messages in this thread | | | Subject | Re: [PATCH 02/10] perf, trace: Use per-tracepoint-per-cpu hlist to track events | From | Peter Zijlstra <> | Date | Fri, 21 May 2010 12:34:03 +0200 |
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On Fri, 2010-05-21 at 12:21 +0200, Frederic Weisbecker wrote: > On Fri, May 21, 2010 at 12:19:09PM +0200, Peter Zijlstra wrote: > > 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 > > > > > Yep. But that also means we need to rcu_dereference_sched() to access > the per cpu list of events.
Why?
The per-cpu vars are allocated and freed in a fully serialized manner, there should be no races what so ever.
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