linux-kernel - Re: [GIT PULL] x86: Put back -pg to tsc.o and add no GCOV to vread_tsc

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Date:	Sat, 28 May 2011 00:14:25 -0400
From:	Andrew Lutomirski <luto@....edu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [GIT PULL] x86: Put back -pg to tsc.o and add no GCOV to vread_tsc_64.o

On Fri, May 27, 2011 at 11:53 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
>
> Ingo,
>
> While running ktest randconfig tests on latest Linus's tree, I hit a
> case where the function graph tracer caused a nasty crash, or even a
> reboot. Using the ktest git bisect utility, I quickly found that the
> crash was due to the commit:
>
>  44259b1a x86-64: Move vread_tsc into a new file with sensible options
>
> I found that it removed the -pg from tsc.o causing accesses to tsc to be
> traced. The function graph tracer uses the tsc outside its recursive
> protection and this caused the crash.

Oops, I didn't think of that.

>
> But this was not the only bug. As I had 3 different configs that crashed
> in my randconfig tests, I tested all three. The first two ran fine with
> the update of the tsc.o with the -pg option, but the third config failed
> with the init process taking a segfault in the vread_tsc function.
>
> That same patch added the vread_tsc_64.o but did not disable GCOV from
> it. Thomas noticed that GCOV was set in that config and after disabling
> GCOV, the strange accesses to kernel space in that function went away.

And that was just an oversight on my part.  Sorry.

> Steven Rostedt (1):
>      x86: Put back -pg to tsc.o and add no GCOV to vread_tsc_64.o

Looks fine to me.

--Andy
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