Date: Mon, 12 Dec 2016 22:34:46 +0100
From: Borislav Petkov <bp@alien8.de>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: x86-ml <x86@kernel.org>, lkml <linux-kernel@vger.kernel.org>,
        Andy Lutomirski <luto@kernel.org>
Subject: Re: WARNING: kernel stack frame pointer at ffffffff82e03f40 in
 swapper:0 has bad value           (null)
Message-ID: <20161212213446.imd3hpt3nudomu7r@pd.tnic>
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On Mon, Dec 12, 2016 at 03:16:27PM -0600, Josh Poimboeuf wrote:
> I still can't figure out what could cause this, nor can I recreate it.

Want my .config?

> Andy, any idea?  I'm trying to figure out why a stack trace of the
> initial task, early in start_kernel(), would show start_cpu() on the
> stack *twice*.  The start_cpu() entry on the stack at ffffffffbce03f50
> is right where it's supposed to be.  But then there's another
> start_cpu() entry at 0xffffffffbce03f48 which is pointed to by the frame
> pointer chain.  I can't figure out where that one came from and why the
> stack is offset by a word, compared to all the other idle task stacks
> I've seen.

Btw, why do you have:

        call    1f              # put return address on stack for unwinder

there in start_cpu() instead of

	push $start_cpu

or so? That CALL looks strange there. If you want to put the return
address, just push start_cpu's address and that's it.

Or am I missing something?

> Boris, what kind of CPU is it?

[    0.169371] smpboot: CPU0: Intel(R) Xeon(R) CPU E5-1620 0 @ 3.60GHz (family: 0x6, model: 0x2d, stepping: 0x7)

Sandybridge. The model 0x2d corresponds to that INTEL_FAM6_SANDYBRIDGE_X
define in intel-family.h.

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.