Bug#988776: Bug#983357: Netinst crashes xen domU when loading kernel

[Chuck Zmudzinski]

On 8/24/2021 7:12 PM, Ben Hutchings wrote:
>
> Text-based sysfs attributes are limited to a page, but udev receives
> uevents through netlink, not sysfs.
>
> The current limit on the environment of a uevent appears to be 2 KB
> (UEVENT_BUFFER_SIZE defined in <linux/kobject.h>).  That seems like it
> *might* be easier to change, so long as user-space doesn't have a
> similar limit.
>
> I looked into systemd/udev, and it seems to use an 8 KB buffer for
> receiving uevents:
>
> https://sources.debian.org/src/systemd/247.9-1/src/libsystemd/sd-device/device-monitor.c/?hl=390#L390
>
> But as a first step I think increasing the kernel buffer size to 4 KB
> would be enough.  Perhaps someone could test whether this patch to the
> domU kernel makes udev happier:
>
> --- a/include/linux/kobject.h
> +++ b/include/linux/kobject.h
> @@ -30,7 +30,7 @@
>   
>   #define UEVENT_HELPER_PATH_LEN		256
>   #define UEVENT_NUM_ENVP			64	/* number of env pointers */
> -#define UEVENT_BUFFER_SIZE		2048	/* buffer for the variables */
> +#define UEVENT_BUFFER_SIZE		4096	/* buffer for the variables */
>   
>   #ifdef CONFIG_UEVENT_HELPER
>   /* path to the userspace helper executed on an event */
> --- END ---
>
> ?
>
> Ben.
>

I tried this patch but the build failed - it ran for over an hour. I am not
sure why as I have not built a Linux kernel in many years. So I will
this:

1) Try to build the unmodified kernel on my system just to be sure I
am building the kernel correctly and that my hardware is OK. Once
I could not build the Linux kernel until I replaced a bad memory
card.

2) If that succeeds, I will try the patch with a bump to the abi version.

 From the output of the failed build and what I read in the section on
the Debian kernel ABI name, I think that the system detected an
ABI change and so it failed. The build was checking symbols when
it failed.

This will take a little while because it takes over an hour to build the
kernel on my system.

Chuck