linux-kernel - Re: [x86] BUG: unable to handle kernel paging request at 00740060

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Date:	Wed, 9 Oct 2013 19:18:11 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Fengguang Wu <fengguang.wu@...el.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [x86] BUG: unable to handle kernel paging request at 00740060


* Ingo Molnar <mingo@...nel.org> wrote:

> 
> * Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Wed, Oct 09, 2013 at 08:19:11PM +0800, Fengguang Wu wrote:
> > > > > Fengguang, I do not think this will help, but just in case. Could you
> > > > > show the result of
> > > > > 
> > > > >         $ kernel/task_work.s
> > > 
> > > Update: I recompiled the kernel with gcc 4.4.7 and find it booting fine!
> > 
> > > # 208 "/c/wfg/tip/arch/x86/include/asm/bitops.h" 1
> > > 	bts $1, 8(%eax); setc %dl	#,, c
> > 
> > That compiler doesn't appear to have asm goto support, so we fall back 
> > to the code we already knew worked :-)
> 
> I'm using 4.7.2 with randconfig testing, which has asm goto support, and 
> I haven't seen this crash yet.
> 
> Unless my testing is off it might be a bug in GCC 4.8, or a pre-existing 
> bug gets exposed by GCC 4.8.

And as it happens, just a few hours later I hit a very similar crash, this 
time compiled with both 4.7.3 and 4.7.2! (config attached)

This has a weird-x86-arch tuning knob as well:

  CONFIG_MGEODE_LX=y

So I think we might need to turn off asm goto for all things 32-bit x86.

Thanks,

	Ingo


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