linux-kernel - Re: PANIC: double fault, error_code: 0x0 in 4.0.0-rc3-2, kvm related?

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Date:	Thu, 19 Mar 2015 01:23:02 +0100
From:	Stefan Seyfried <stefan.seyfried@...glemail.com>
To:	Andy Lutomirski <luto@...capital.net>
CC:	Jiri Kosina <jkosina@...e.cz>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Takashi Iwai <tiwai@...e.de>, X86 ML <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>, Tejun Heo <tj@...nel.org>
Subject: Re: PANIC: double fault, error_code: 0x0 in 4.0.0-rc3-2, kvm related?

Am 19.03.2015 um 00:22 schrieb Andy Lutomirski:
> On Wed, Mar 18, 2015 at 3:40 PM, Andy Lutomirski <luto@...capital.net> wrote:
>> Yes, it's userspace.  Thanks for checking, though.
> 
> One more stupid hunch:
> 
> Can you do:
> x/21xg ffff8801013d4f58
> 
> If I counted right, that'll dump task_pt_regs(current).

That's all zeroes:
crash> x /21xg 0xffff8801013d4f58
0xffff8801013d4f58:     0x0000000000000000      0x0000000000000000
0xffff8801013d4f68:     0x0000000000000000      0x0000000000000000
0xffff8801013d4f78:     0x0000000000000000      0x0000000000000000
0xffff8801013d4f88:     0x0000000000000000      0x0000000000000000
0xffff8801013d4f98:     0x0000000000000000      0x0000000000000000
0xffff8801013d4fa8:     0x0000000000000000      0x0000000000000000
0xffff8801013d4fb8:     0x0000000000000000      0x0000000000000000
0xffff8801013d4fc8:     0x0000000000000000      0x0000000000000000
0xffff8801013d4fd8:     0x0000000000000000      0x0000000000000000
0xffff8801013d4fe8:     0x0000000000000000      0x0000000000000000
0xffff8801013d4ff8:     0x0000000000000000

But maybe you counted wrong (or I'm reading arch/x86/include/asm/processor.h wrong, which is at least as likely...).

#define task_pt_regs(tsk)  ((struct pt_regs *)(tsk)->thread.sp0 - 1)

=> I have the task_struct readily available decoded in the crash utility.

crash> task, search for thread, in thread:
     sp0 = 18446612136629993472
crash> eval 18446612136629993472
hexadecimal: ffff8801013d8000  (18014269664677728KB)
....
crash> print *(struct pt_regs *)(18446612136629993472 - sizeof(struct pt_regs))
$20 = {
  r15 = 18446744071585666077, 
  r14 = 16, 
  r13 = 582, 
  r12 = 18446612136629993352, 
  bp = 24, 
  bx = 18446744071585666061, 
  r11 = 582, 
  r10 = 10760856, 
  r9 = 140712613762160, 
  r8 = 140735967861216, 
  ax = 1, 
  cx = 140712476030103, 
  dx = 140712613782304, 
  si = 1, 
  di = 140712589295616, 
  orig_ax = 209, 
  ip = 140712571864823, 
  cs = 51, 
  flags = 582, 
  sp = 140735967860552, 
  ss = 43
}

=>
r15 = ffffffff8168141d
r12 = ffff8801013d7f88
bx  = ffffffff8168140d
r9  = 7ffa355bd470
ip  = 7ffa32dc86f7
sp  = 7fffa55f1748

looks somehow legit, to my totally untrained eye (ip and sp actually).

I'm off to bed now (01:20 around here ;), will be back in about 7 hours.

Best regards,

	Stefan
-- 
Stefan Seyfried
Linux Consultant & Developer -- GPG Key: 0x731B665B

B1 Systems GmbH
Osterfeldstraße 7 / 85088 Vohburg / http://www.b1-systems.de
GF: Ralph Dehner / Unternehmenssitz: Vohburg / AG: Ingolstadt,HRB 3537
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