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

On jeu., août 04 2016, Russell King - ARM Linux <linux@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@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@free-electrons.com>

Thanks,

Gregory

>
> --
> RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
> FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
> according to speedtest.net.
>
> _______________________________________________
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--
Gregory Clement, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com

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