linux-kernel - Re: [PATCH] Sometimes, there is OOPS happened when we use oprofile.

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Date:	Wed, 31 Oct 2012 23:45:23 +0100
From:	Robert Richter <rric@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	"Zhang, Jun" <jun.zhang@...el.com>, Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"x86@...nel.org" <x86@...nel.org>,
	"oprofile-list@...ts.sf.net" <oprofile-list@...ts.sf.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH] Sometimes, there is OOPS happened when we use oprofile.

On 31.10.12 14:33:17, H. Peter Anvin wrote:
> I'm vaguely concerned about the following:
> 
> + * To always return a non-null
> + * stack pointer we fall back to regs as stack if no previous stack
> + * exists.
> 
> The logic being that if there is no stack pointer and the stack is
> too empty, to simply assume regs point to the top of the stack?  Is
> this possible to ever be actually seen?

I discussed this with Steven too (https://lkml.org/lkml/2012/9/6/322)
and we both had a bad feeling with returning a null pointer by
kernel_stack_pointer() (implemented in version 1 of this patch). It
could be null if tinfo->previous_esp is null (last stack). Not sure
when this may happen.

So using regs as fallback seemed to be ok as this was in for years:

 7b6c6c7 x86, 32-bit: fix kernel_trap_sp()

-Robert
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