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

From: Gregory CLEMENT <gregory.clement@free-electrons.com>
To: Russell King - ARM Linux <linux@armlinux.org.uk>
Cc: Guenter Roeck <linux@roeck-us.net>,
	Will Deacon <will.deacon@arm.com>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-arm-kernel\@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: "Failed to create /dev/root: -14" after commit e6978e4bf1 ("ARM: save and reset the address limit when entering an exception")
Date: Tue, 09 Aug 2016 17:06:51 +0200	[thread overview]
Message-ID: <87eg5y3rsk.fsf@free-electrons.com> (raw)
In-Reply-To: <20160804100748.GP1041@n2100.armlinux.org.uk> (Russell King's message of "Thu, 4 Aug 2016 11:07:48 +0100")

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

>
> -- 
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-- 
Gregory Clement, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com