linux-kernel - Re: BUG uncore_assign

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Message-ID: <20140910215908.GL4120@two.firstfloor.org>
Date:	Wed, 10 Sep 2014 23:59:08 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	Stephane Eranian <eranian@...gle.com>,
	Ingo Molnar <mingo@...nel.org>,
	Vince Weaver <vincent.weaver@...ne.edu>
Subject: Re: BUG uncore_assign_events

> # addr2line -i -e ivb-ep-build/vmlinux ffffffff81025f18
> 
> arch/x86/include/asm/bitops.h:318
> arch/x86/kernel/cpu/perf_event_intel_uncore.c:3339

i == zero  (ok)
c points to some kernel looking address
hwc->idx is 64

     /* fastpath, try to reuse previous register */
        for (i = 0; i < n; i++) {
                hwc = &box->event_list[i]->hw;
                c = hwc->constraint;

                /* never assigned */
                if (hwc->idx == -1)
                        break;

                /* constraint still honored */
                if (!test_bit(hwc->idx, c->idxmsk))
                        break;

My best bet is something goes wrong in uncore_pmu_to_box or
uncore_event_to_pmu in hte caller, so the box is bogus.

Did the test do CPU hot plug?

BTW i don't think it's a security issue because the uncore driver
is only accesible for root.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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