linux-kernel - Re: Linux 4.4.256

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Date:   Fri, 5 Feb 2021 12:56:58 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        torvalds@...ux-foundation.org, stable@...r.kernel.org, lwn@....net,
        jslaby@...e.cz, shuah@...nel.org, patches@...nelci.org,
        lkft-triage@...ts.linaro.org, pavel@...x.de, jonathanh@...dia.com
Subject: Re: Linux 4.4.256

On Fri, Feb 05, 2021 at 03:26:36PM +0100, Greg Kroah-Hartman wrote:
> I'm announcing the release of the 4.4.256 kernel.
> 
> This, and the 4.9.256 release are a little bit "different" than normal.
> 
> This contains only 1 patch, just the version bump from .255 to .256 which ends
> up causing the userspace-visable LINUX_VERSION_CODE to behave a bit differently
> than normal due to the "overflow".
> 
> With this release, KERNEL_VERSION(4, 4, 256) is the same as KERNEL_VERSION(4, 5, 0).
> 
> Nothing in the kernel build itself breaks with this change, but given that this
> is a userspace visible change, and some crazy tools (like glibc and gcc) have
> logic that checks the kernel version for different reasons, I wanted to do this
> release as an "empty" release to ensure that everything still works properly.
> 
> So, this is a YOU MUST UPGRADE requirement of a release.  If you rely on the
> 4.4.y kernel, please throw this release into your test builds and rebuild the
> world and let us know if anything breaks, or if all is well.
> 
> Go forth and do full system rebuilds!  Yocto and Gentoo are great for this, as
> will systems that use buildroot.
> 
> I'll try to hold off on doing a "real" 4.4.y release for a week to give
> everyone a chance to test this out and get back to me.  The pending patches in
> the 4.4.y queue are pretty serious, so I am loath to wait longer than that,
> consider yourself warned...
> 
Thanks a lot for the heads-up. For chromeos-4.4, the version number wrap
is indeed fatal: Unfortunately we have lots of vendor code in the tree
which uses KERNEL_VERSION(), and all the version comparisons against
KERNEL_VERSION(4,5,0) do result in compile errors.

The best workaround/hack/kludge to address the problem seems to be the idea
to use 4.4.255 as version number for LINUX_VERSION_CODE and KERNEL_VERSION()
if SUBLEVEL is larger than 255. Did anyone find a better solution for the
problem ?

Thanks,
Guenter