Re: perf: fuzzer triggered warning in intel_pmu_drain_pebs_nhm()

From	Stephane Eranian <eranian@googlemail.com>
Newsgroups	linux.kernel
Subject	Re: perf: fuzzer triggered warning in intel_pmu_drain_pebs_nhm()
Date	2015-07-15 08:50 +0200
Message-ID	<pMoFY-83L-25@gated-at.bofh.it> (permalink)
References	<pHOrn-4pb-9@gated-at.bofh.it> <pI92O-xt-5@gated-at.bofh.it> <pIelQ-3Gi-7@gated-at.bofh.it> <pIevw-3YV-9@gated-at.bofh.it> <pIf8e-4d6-23@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Fri, Jul 3, 2015 at 9:49 PM, Vince Weaver <vincent.weaver@maine.edu> wrote:
> On Fri, 3 Jul 2015, Peter Zijlstra wrote:
>
>> That said, its far too warm and I might just not be making sense.
>
> you need to come visit Maine!  Although I am not sure the cooler weather
> necessarily improves my kernel debugging skills.
>
> I managed to lock the machine (again this is with the patch applied).
>
I can reproduce the problem on my HSW running the fuzzer.

I can see why this could be happening if you are mixing PEBS and non PEBS events
in the bottom 4 counters. I suspect:
        for (bit = 0; bit < x86_pmu.max_pebs_events; bit++) {
                if ((counts[bit] == 0) && (error[bit] == 0))
                        continue;

This test is not correct when you have non-PEBS events mixed with PEBS
events and
they overflow at the same time. They will have counts[i] != 0 but
error[i] == 0, and thus
you fall thru the loop and hit the assert. Or it is something along those lines.


> [  299.366027] ------------[ cut here ]------------
> [  299.370985] WARNING: CPU: 2 PID: 8241 at arch/x86/kernel/cpu/perf_event_intel_ds.c:1198 intel_pmu_drain_pebs_nhm+0x283/0x2e0()
> [  299.456929] CPU: 2 PID: 8241 Comm: perf_fuzzer Tainted: G        W       4.1.0+ #164
> [  299.465750] Hardware name: LENOVO 10AM000AUS/SHARKBAY, BIOS FBKT72AUS 01/26/2014
> [  299.474274]  ffffffff81a105a0 ffff88011ea85b10 ffffffff8169f823 0000000000000000
> [  299.482864]  0000000000000000 ffff88011ea85b50 ffffffff8106ec8a ffff88011ea85ba0
> [  299.491488]  0000000000000000 0000000000000001 ffff88011ea8bd80 ffff8801190400c0
> [  299.500029] Call Trace:
> [  299.503190]  <NMI>  [<ffffffff8169f823>] dump_stack+0x45/0x57
> [  299.509936]  [<ffffffff8106ec8a>] warn_slowpath_common+0x8a/0xc0
> [  299.516901]  [<ffffffff8106ed7a>] warn_slowpath_null+0x1a/0x20
> [  299.523715]  [<ffffffff8102f783>] intel_pmu_drain_pebs_nhm+0x283/0x2e0
> [  299.531268]  [<ffffffff81032235>] intel_pmu_handle_irq+0x255/0x440
> [  299.538487]  [<ffffffff81028e76>] perf_event_nmi_handler+0x26/0x40
> [  299.545638]  [<ffffffff810181ad>] nmi_handle+0x9d/0x140
> [  299.551772]  [<ffffffff81018115>] ? nmi_handle+0x5/0x140
> [  299.558013]  [<ffffffff8101843a>] default_do_nmi+0x4a/0x120
> [  299.564527]  [<ffffffff8101859d>] do_nmi+0x8d/0xc0
> [  299.570185]  [<ffffffff816a979f>] end_repeat_nmi+0x1e/0x2e
> [  299.576580]  [<ffffffff811bc9d2>] ? check_poison_obj+0x92/0x230
> [  299.583390]  [<ffffffff811bc9d2>] ? check_poison_obj+0x92/0x230
> [  299.590163]  [<ffffffff811bc9d2>] ? check_poison_obj+0x92/0x230
> [  299.596922]  <<EOE>>  [<ffffffff8115bea8>] ? perf_event_alloc+0x58/0x680
> [  299.604594]  [<ffffffff811bcf7d>] cache_alloc_debugcheck_after.isra.51+0x1cd/0x250
> [  299.613140]  [<ffffffff811c08b6>] kmem_cache_alloc_trace+0xa6/0x510
> [  299.620330]  [<ffffffff8115bea8>] ? perf_event_alloc+0x58/0x680
> [  299.627088]  [<ffffffff8106ee48>] ? get_online_cpus+0x58/0x70
> [  299.633688]  [<ffffffff8115bea8>] perf_event_alloc+0x58/0x680
> [  299.640319]  [<ffffffff8115c897>] SYSC_perf_event_open+0x3c7/0xd40
> [  299.647353]  [<ffffffff8105f86b>] ? __do_page_fault+0x1ab/0x3f0
> [  299.654172]  [<ffffffff8115d689>] SyS_perf_event_open+0x9/0x10
> [  299.660871]  [<ffffffff816a7572>] entry_SYSCALL_64_fastpath+0x16/0x7a
> [  299.668236] ---[ end trace 3356c74581c13f1d ]---
> [  299.673648] Uhhuh. NMI received for unknown reason 31 on CPU 2.
> [  299.680427] Do you have a strange power saving mode enabled?
> [  299.686963] Dazed and confused, but trying to continue
> [  299.692904] Uhhuh. NMI received for unknown reason 31 on CPU 2.
> [  299.699748] Do you have a strange power saving mode enabled?
> [  299.706227] Dazed and confused, but trying to continue
> [  299.712172] Uhhuh. NMI received for unknown reason 31 on CPU 2.
> [  299.718946] Do you have a strange power saving mode enabled?
> [  299.725446] Dazed and confused, but trying to continue
> [  299.731419] Uhhuh. NMI received for unknown reason 31 on CPU 2.
> [  299.738235] Do you have a strange power saving mode enabled?
> [  299.744740] Dazed and confused, but trying to continue
> [  299.750660] Uhhuh. NMI received for unknown reason 21 on CPU 2.
> [  299.757398] Do you have a strange power saving mode enabled?
> [  299.763862] Dazed and confused, but trying to continue
>
> (machine eventually locks up after lots of these messages)
>
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Re: perf: fuzzer triggered warning in intel_pmu_drain_pebs_nhm() Stephane Eranian <eranian@googlemail.com> - 2015-07-15 08:50 +0200
  Re: perf: fuzzer triggered warning in intel_pmu_drain_pebs_nhm() Peter Zijlstra <peterz@infradead.org> - 2015-07-15 14:40 +0200
    Re: perf: fuzzer triggered warning in intel_pmu_drain_pebs_nhm() Stephane Eranian <eranian@googlemail.com> - 2015-07-16 23:20 +0200

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