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 16:22:16 +0100
From:	Takashi Iwai <tiwai@...e.de>
To:	Denys Vlasenko <vda.linux@...glemail.com>
Cc:	Denys Vlasenko <dvlasenk@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Jiri Kosina <jkosina@...e.cz>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Stefan Seyfried <stefan.seyfried@...glemail.com>,
	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?

At Thu, 19 Mar 2015 15:55:26 +0100,
Takashi Iwai wrote:
> 
> At Thu, 19 Mar 2015 14:47:12 +0100,
> Takashi Iwai wrote:
> > 
> > At Thu, 19 Mar 2015 13:48:56 +0100,
> > Denys Vlasenko wrote:
> > > 
> > > Having no more ideas at the moment, here is a tarball of 13 patches
> > > of commits touching entry_64.S up to 4.0.0-rc1.
> > > 
> > > x0001.patch is the latest, x0015.patch is the oldest.
> > > 
> > > Patches 0003 and 0008 are not there since 0003 is empty merge patch
> > > and 0008 does some PCI fixup.
> > > 
> > > If this breakage is recent, it ought to be one of these.
> > > Most of them do some non-trivial surgery.
> > > 
> > > Even though I did not spot anything suspicious in them,
> > > entry.S is notorious for subtle breakage.
> > > 
> > > Try reverting them in sequence starting from x0001.patch
> > > and see reverting which one makes crash disappear.
> > 
> > OK, I'm going to check these git series.
> 
> Reverting the commit
> 96b6352c12711d5c0bb7157f49c92580248e8146
>     x86_64, entry: Remove the syscall exit audit and schedule optimizations
> 
> seems enough.  After reverting this one, the machine runs stable with
> the kvm stress test.
> 
> (I'll keep test running for a while; at the previous bisection, I hit
>  the bug right after posting the mail ;)

It survived long enough, so this looks like the spot.

Also, I checked the patch below instead of reverting the commit, and
this seems working, too.


Takashi

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 1d74d161687c..5340ac7f88a9 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -364,12 +364,12 @@ system_call_fastpath:
  * Has incomplete stack frame and undefined top of stack.
  */
 ret_from_sys_call:
-	testl $_TIF_ALLWORK_MASK,TI_flags+THREAD_INFO(%rsp,RIP-ARGOFFSET)
-	jnz int_ret_from_sys_call_fixup	/* Go the the slow path */
-
 	LOCKDEP_SYS_EXIT
 	DISABLE_INTERRUPTS(CLBR_NONE)
 	TRACE_IRQS_OFF
+	testl $_TIF_ALLWORK_MASK,TI_flags+THREAD_INFO(%rsp,RIP-ARGOFFSET)
+	jnz int_ret_from_sys_call_fixup	/* Go the the slow path */
+
 	CFI_REMEMBER_STATE
 	/*
 	 * sysretq will re-enable interrupts:
--
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