On 08/09/2012 08:51 AM, Stephane Eranian wrote: > Hi, > > I ran into a problem on my AMD box whereby I would hit the > WARN_ON_ONCE(cpuctx->cgrp) in perf_cgroup_switch(). > > It took me a while to track this down. It turns out that the > list_for_each_entry_rcu() loop had multiple iterations. That's > normal, we have CPU PMU and IBS PMU. But what caused > the warning to fire is that both the core and IBS PMU were > pointing to the same cpuctx struct. Thus, the cpuctx->cgrp > was already set in the second iteration. > > Is the warning a false positive?
I think it's a false positive, I'm not sure. > > In perf_pmu_register(), there is a search for a matching > pmu->task_ctx_nr. Given that the field is pointing to > perf_hw_context for both cpu and IBS PMU, there is > a match and therefore the cpuctx are shared. > > The question is: why do we have to share the cpuctx? > > Note that the same issue probably exists with the Intel > uncore PMU. uncore PMU does not have this issue because uncore_pmu->task_ctx_nr is 'perf_invalid_context'. find_pmu_context() always return NULL in that case. Regards Yan, Zheng. > > If we need to share, then the perf_cgroup_switch() code > needs to change because, as it stands, it is doing the > switching twice in this case. > > Either way something looks wrong here. > > Any idea? > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
