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

[Kevin Hilman]

On Tue, Aug 9, 2016 at 10:06 AM, Gregory CLEMENT
<gregory.clement at free-electrons.com> wrote:
> Hi Russell King,
>
>  On jeu., août 04 2016, Russell King - ARM Linux <linux at armlinux.org.uk> wrote:
>
>> 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 at roeck-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.
>
> The Armada XP base platform were hit by the same bug as we can see on
> kernlci:
> https://storage.kernelci.org/mainline/v4.8-rc1/arm-mvebu_v7_defconfig/lab-baylibre-seattle/boot-armada-xp-openblocks-ax3-4.html
>
> Your patch solves the issue too.
>
> Will you push this patch for v4.8-rc2 ?
>
> Also I wonder if it is something expected to have this issue on a "real"
> hardware.
>
> You can also add my:
> Tested-by: Gregory CLEMENT <gregory.clement at free-electrons.com>

I also tested this fixes the boot issue on Armada XP.

Tested-by: Kevin Hilman <khilman at baylibre.com>

Kevin