Bug 916132

Summary:	sys-apps/kmod-31 cannot load XZ compressed modules
Product:	Gentoo Linux	Reporter:	Victor Mataré <vmatare+gbug>
Component:	Current packages	Assignee:	Gentoo's Team for Core System packages <base-system>
Status:	RESOLVED FIXED
Severity:	critical	CC:	dist-kernel, ionen, kernel, sam
Priority:	Normal
Version:	unspecified
Hardware:	All
OS:	Linux
URL:	https://lore.kernel.org/all/df84e672-81f2-4f48-a5cf-65eb05ecc242@moonlit-rail.com/T/
See Also:	https://bugs.debian.org/1050582 https://bugs.debian.org/1050586 https://bugs.gentoo.org/show_bug.cgi?id=920837
Whiteboard:
Package list:		Runtime testing required:	---

Description Victor Mataré 2023-10-22 16:29:42 UTC

Apparently kmod-31 does not really work with kernels that set MODULE_COMPRESS_XZ:

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1050582

According to the debian bug they switched to the in-kernel XZ implementation with v31, but the in-kernel XZ implementation has some severe limitations that make it unable to deal with larger modules.

From what I've read so far, other module compression algos should be fine, but haven't tested it, yet.

Comment 1 Victor Mataré 2023-10-22 16:31:04 UTC

Added a kernel lore link that mentions a kernel patch which should remedy the situation.

Comment 2 Sam James archtester

2023-10-22 16:32:30 UTC

Not disputing the bug at all, I just wanted to note that I use MODULE_COMPRESS_XZ on two machines and nothing exploded there, which is curious.

Thanks for the report - someone had made a reference to kmod-31 not working but didn't give any more detail and I couldn't figure out what was going on there.

Comment 3 Sam James archtester

2023-10-28 00:27:42 UTC

mpagano put https://gitweb.gentoo.org/proj/linux-patches.git/commit/?h=6.5&id=51bcb2538941016f4ebd47dcc0c878f26a105a0c into genpatches so we should be good now.

Comment 4 Ionen Wolkens gentoo-dev

2023-12-28 06:22:01 UTC

ftr, got fixed anyway but see there was problems reproducing the issue here and, while looking at similar bug #920837 I couldn't either. It turned out need to set CONFIG_MODULE_DECOMPRESS=y.

It's also not a default ("if unsure, say N"), nor is it set for gentoo-kernel I can see, and kmod-31 NEWS mentions it needs kernel >=6.4 to work. So it should only have affected a few people in ~arch that manually enabled it.

Wasn't clear to me at first given I didn't know the option existed (thought only needed XZ decompression support), so thought I'd note it here.