linux-kernel - Re: BUG uncore_assign

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Date:	Thu, 11 Sep 2014 00:29:56 -0500
From:	Chuck Ebbert <cebbert.lkml@...il.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Peter Zijlstra <peterz@...radead.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

On Wed, 10 Sep 2014 23:59:08 +0200
Andi Kleen <andi@...stfloor.org> wrote:

> > # 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;
> 

hwc->idx is not 64 -- it's 0xd000064

The bt insn is causing a page fault 27 MB past c->idxmsk
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