On 3/16/2021 3:22 AM, Namhyung Kim wrote:
Hi Peter and Kan,
On Thu, Mar 4, 2021 at 5:22 AM Peter Zijlstra peterz@infradead.org wrote:
On Wed, Mar 03, 2021 at 02:53:00PM -0500, Liang, Kan wrote:
On 3/3/2021 1:59 PM, Peter Zijlstra wrote:
On Wed, Mar 03, 2021 at 05:42:18AM -0800, kan.liang@linux.intel.com wrote:
+++ b/arch/x86/events/intel/ds.c @@ -2000,18 +2000,6 @@ static void intel_pmu_drain_pebs_nhm(struct pt_regs *iregs, struct perf_sample_d continue; }
/** On some CPUs the PEBS status can be zero when PEBS is* racing with clearing of GLOBAL_STATUS.** Normally we would drop that record, but in the* case when there is only a single active PEBS event* we can assume it's for that event.*/if (!pebs_status && cpuc->pebs_enabled &&!(cpuc->pebs_enabled & (cpuc->pebs_enabled-1)))pebs_status = cpuc->pebs_enabled;Wouldn't something like:
pebs_status = p->status = cpus->pebs_enabled;I didn't consider it as a potential solution in this patch because I don't think it's a proper way that SW modifies the buffer, which is supposed to be manipulated by the HW.
Right, but then HW was supposed to write sane values and it doesn't do that either ;-)
It's just a personal preference. I don't see any issue here. We may try it.
So I mostly agree with you, but I think it's a shame to unsupport such chips, HSW is still a plenty useable chip today.
I got a similar issue on ivybridge machines which caused kernel crash. My case it's related to the branch stack with PEBS events but I think it's the same issue. And I can confirm that the above approach of updating p->status fixed the problem.
I've talked to Stephane about this, and he wants to make it more robust when we see stale (or invalid) PEBS records. I'll send the patch soon.
Hi Namhyung,
In case you didn't see it, I've already submitted a patch to fix the issue last Friday. https://lore.kernel.org/lkml/1615555298-140216-1-git-send-email-kan.liang@li... But if you have a more robust proposal, please feel free to submit it.
BTW: The patch set from last Friday also fixed another bug found by the perf_fuzzer test. You may be interested.
Thanks, Kan