linux-kernel - Re: [perf] perf top segfaulting

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Date:	Fri, 3 Feb 2012 20:46:23 -0600
From:	Dan McGee <dpmcgee@...il.com>
To:	David Daney <david.daney@...ium.com>
Cc:	linux-kernel@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [perf] perf top segfaulting

On Fri, Feb 3, 2012 at 8:24 PM, David Daney <david.daney@...ium.com> wrote:
> On 02/03/2012 04:45 PM, Dan McGee wrote:
>>
>> On i686, version 3.2-2, but looks like annotate.c hasn't changed much
>> since. It sometimes happens within 5 seconds of starting perf,
>> sometimes much later, but almost always if I leave it running I well
>> come back to it having segfaulted. When ran with gdb here it took
>> about 3 minutes; I had a 5 second segfault and a 5 minute segfault
>> before and after this run as well. I'm not sure what triggers it other
>> than it isn't user input, as I can start `perf top`, not touch it, and
>> it will eventually segfault.
>>
>
>
> I have seen the same thing (basically the same stack trace), so I think what
> I see is probably closely related.  My failures however are on mips64 based
> systems.
>
> My debugging suggests that this happens when the ABIs used by the running
> processes are heterogeneous (A mixture of 32-bit and 64-bit processes).
>  What I see is that all processes use a library with a common name, but
> differing in paths (/lib32/libc-2.11.3.so and /lib64/libc-2.11.3.so for
> example).  It looks like perf is confusing the offsets it caches from one
> library to look up information in the other and since the symbols are in
> different locations, the resulting erroneous address calculations result in
> accesses to unmapped portions of perf's address space and you get SIGSEGV.
>
> I haven't dug into the code enough to suggest a fix, but I think that at a
> high hand-waving level, this is what is happening.  I have never observed
> the failure when using only a single ABI on the system

Note that in this case, it is a pure 32-bit x86 system, and no library
changes were going on in the background. So I wouldn't be surprised if
the causes are similar (or the same), but I don't think I can chalk it
up to being a single ABI vs multiple ABI problem; i686 only has one
ABI.

-Dan
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