linux-kernel - Re: [BUG] perf: bogus correlation of kernel symbols

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Message-ID: <BANLkTi==OatTqfDbnAmHQA0t2DmokEd-CA@mail.gmail.com>
Date:	Thu, 12 May 2011 13:31:37 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	Arnaldo Carvalho de Melo <acme@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [BUG] perf: bogus correlation of kernel symbols

On Thu, May 12, 2011 at 7:48 AM, Stephane Eranian <eranian@...gle.com> wrote:
>
> I think there is a serious problem with kernel symbol correlation
> with the latest perf in 2.6.39-rc7-tip.

Yeah. It's annoying. It's a "perf" bug, though - triggered by
/proc/sys/kernel/kptr_restrict being set to 1.

The bug is that perf doesn't say "I can't match kernel symbols", but
instead does some crazy matching and gives total crap module
information (I think it just picks the one that shows up last in
/proc/kallsyms).

That said, I have considered just reverting the thing that makes
kptr_restrict be 1 by default. I do like the security implications of
restricting visibility into kernel pointers, but I also think that
security rules that make the system less usable are dubious. So I
dunno.

                           Linus
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