Messages in this thread | | | Date | Thu, 9 Aug 2012 16:05:09 +0200 | Subject | Re: [BUG] perf: sharing of cpuctx between core and ibs PMU causes problems | From | Stephane Eranian <> |
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On Thu, Aug 9, 2012 at 8:55 AM, Yan, Zheng <zheng.z.yan@intel.com> wrote: > 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. > Well, but then you're doing the same work twice.
>> >> 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. > Yes, I think IBS should do the same and that should fix the problem there too. Will try that.
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