Re: [PATCH v7 16/25] arm: Add support for generic vDSO (causing crash)

Vincenzo Frascino
2019-12-04T17:13:04Z

Hi Guenter,

On 12/4/19 4:16 PM, Guenter Roeck wrote:
> On Wed, Dec 04, 2019 at 01:58:25PM +0000, Vincenzo Frascino wrote:
>> Hi Guenter,
>>
>> On 12/4/19 1:51 PM, Guenter Roeck wrote:
>>> On Fri, Jun 21, 2019 at 10:52:43AM +0100, Vincenzo Frascino wrote:
>>>> The arm vDSO library requires some adaptations to use to take advantage
>>>> of the newly introduced generic vDSO library.
>>>>
>>>> Introduce the following changes:
>>>> - Modification vdso.c to be compliant with the common vdso datapage
>>>> - Use of lib/vdso for gettimeofday
>>>> - Implementation of elf note
>>>>
>>>> Cc: Russell King <linux@armlinux.org.uk>
>>>> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
>>>
>>> This patch causes a crash with qemu's mcimx6ul-evk emulation while running
>>> imx_v6_v7_defconfig.
>>>
>>
>> Thank you for reporting this. Could you please provide some details on how I can
>> reproduce the scenario you are describing?
>>
> - Build imx_v6_v7_defconfig
> - Get root file system or initrd, for example from
> https://github.com/groeck/linux-build-test/tree/master/rootfs/arm
> - Run image. Example, with initrd:
> qemu-system-arm -M mcimx6ul-evk -kernel arch/arm/boot/zImage \
> -no-reboot -initrd rootfs-armv7a.cpio \
> -m 256 -display none -serial null \
> --append 'rdinit=/sbin/init earlycon=ec_imx6q,mmio,0x21e8000,115200n8 console=ttymxc1,115200'
> -dtb arch/arm/boot/dts/imx6ul-14x14-evk.dtb \
> -nographic -monitor null -serial stdio
>
> qemu has to be v3.1 or later to support the machine.
>

Thanks for this. Could you please try the patch below the scissors? Seems fixing
the issue for me.

> Hope this helps,
> Guenter
>

--
Regards,
Vincenzo

--->8---

Author: Vincenzo Frascino <vincenzo.frascino@arm.com>
Date: Wed Dec 4 16:58:55 2019 +0000

arm: Fix __arch_get_hw_counter() access to CNTVCT

__arch_get_hw_counter() should check clock_mode to see if it can access
CNTVCT. With the conversion to unified vDSO this check has been left out.

This causes on imx v6 and v7 (imx_v6_v7_defconfig) and other platforms to
hang at boot during the execution of the init process as per below:

[ 19.976852] Run /sbin/init as init process
[ 20.044931] Kernel panic - not syncing: Attempted to kill init!
exitcode=0x00000004

Fix the problem verifying that clock_mode is set coherently before
accessing CNTVCT.

Cc: Russell King <linux@armlinux.org.uk>
Reported-by: Guenter Roeck <linux@roeck-us.net>
Investigated-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>

diff --git a/arch/arm/include/asm/vdso/gettimeofday.h
b/arch/arm/include/asm/vdso/gettimeofday.h
index 5b879ae7afc1..0ad2429c324f 100644
--- a/arch/arm/include/asm/vdso/gettimeofday.h
+++ b/arch/arm/include/asm/vdso/gettimeofday.h
@@ -75,6 +75,9 @@ static __always_inline u64 __arch_get_hw_counter(int clock_mode)
#ifdef CONFIG_ARM_ARCH_TIMER
u64 cycle_now;

+ if (!clock_mode)
+ return -EINVAL;
+
isb();
cycle_now = read_sysreg(CNTVCT);