linux-kernel - Re: "Failed to create /dev/root: -14" after commit e6978e4bf1 ("ARM: save and reset the address limit when entering an exception")

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Message-ID: <20160804100748.GP1041@n2100.armlinux.org.uk>
Date:	Thu, 4 Aug 2016 11:07:48 +0100
From:	Russell King - ARM Linux <linux@...linux.org.uk>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Will Deacon <will.deacon@....com>
Subject: Re: "Failed to create /dev/root: -14" after commit e6978e4bf1 ("ARM:
 save and reset the address limit when entering an exception")

On Wed, Aug 03, 2016 at 08:07:02AM -0700, Guenter Roeck wrote:
> On 08/03/2016 01:38 AM, Russell King - ARM Linux wrote:
> >On Tue, Aug 02, 2016 at 07:51:45PM -0700, Guenter Roeck wrote:
> >>Hi,
> >>
> >>I see the following crash when running a qemu arm 'kzm' runtime test with
> >>the current mainline.
> >>...
> >>Failed to create /dev/root: -14
> >>
> >>[ followed by panic ]
> >>
> >>A complete log file is at [1].
> >
> >I think it's because of those undefined instructions you're hitting
> >with the hw-breakpoint code... can you try the patch below please?
> >
> >  arch/arm/kernel/entry-armv.S | 1 +
> >  1 file changed, 1 insertion(+)
> >
> >diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
> >index bc5f50799d75..9f157e7c51e7 100644
> >--- a/arch/arm/kernel/entry-armv.S
> >+++ b/arch/arm/kernel/entry-armv.S
> >@@ -295,6 +295,7 @@ __und_svc_fault:
> >  	bl	__und_fault
> >
> >  __und_svc_finish:
> >+	get_thread_info tsk
> >  	ldr	r5, [sp, #S_PSR]		@ Get SVC cpsr
> >  	svc_exit r5				@ return from exception
> >   UNWIND(.fnend		)
> >
> 
> Yes, that fixes the problem.
> 
> Assuming you'll create a patch:
> 
> Tested-by: Guenter Roeck <linux@...ck-us.net>
> 
> Does that need to be addressed in qemu, or is it a Linux bug ?

It's a Linux bug provoked by qemu not implementing the hardware
breakpoints.  Well worth fixing in Linux.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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