[Bug 2032674] [NEW] failed to load large compressed kernel modules in mantic with 6.5

[Andrea Righi]

Public bug reported:

[Impact]

Kernel 6.5 in Mantic enabled zstd module compression and at the same
time libkmod is now trying to decompress the modules in-kernel directly.
However the size that can be allocated by the kernel to do such
decompression is limited and some large modules can fail to load (such
as zfs for example).

[Test case]

Install zfs-dkms, then run:

 $ modprobe zfs

[Fix]

Fallback to the old user-space module loading way when ENOMEM is
returned by finit_module().

[Regression potential]

We may introduce a small performance regression when loading multiple
modules, due to the in-kernel and user-space attempts to load kernel
modules, however this performance regression is negligible (one
additional syscall when loading large modules) and it allows to
correctly support large compressed kernel modules.

ProblemType: Bug
DistroRelease: Ubuntu 23.10
Package: kmod 30+20230519-1ubuntu2
ProcVersionSignature: User Name 6.5.0-6.6-generic 6.5.0-rc7
Uname: Linux 6.5.0-6-generic x86_64
ApportVersion: 2.27.0-0ubuntu2
Architecture: amd64
CasperMD5CheckResult: unknown
CloudArchitecture: x86_64
CloudBuildName: server
CloudID: nocloud
CloudName: unknown
CloudPlatform: nocloud
CloudSerial: 20230822
CloudSubPlatform: config-disk (/dev/vdb)
Date: Tue Aug 22 15:31:34 2023
ProcEnviron:
 LANG=C.UTF-8
 PATH=(custom, no user)
 SHELL=/bin/bash
 TERM=xterm-256color
 XDG_RUNTIME_DIR=<set>
SourcePackage: kmod
UpgradeStatus: No upgrade log present (probably fresh install)

** Affects: kmod (Ubuntu)
     Importance: Undecided
         Status: New

** Affects: kmod (Ubuntu Mantic)
     Importance: Undecided
         Status: New


** Tags: amd64 apport-bug cloud-image mantic

** Also affects: kmod (Ubuntu Mantic)
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/2032674

Title:
  failed to load large compressed kernel modules in mantic with 6.5

Status in kmod package in Ubuntu:
  New
Status in kmod source package in Mantic:
  New

Bug description:
  [Impact]

  Kernel 6.5 in Mantic enabled zstd module compression and at the same
  time libkmod is now trying to decompress the modules in-kernel
  directly. However the size that can be allocated by the kernel to do
  such decompression is limited and some large modules can fail to load
  (such as zfs for example).

  [Test case]

  Install zfs-dkms, then run:

   $ modprobe zfs

  [Fix]

  Fallback to the old user-space module loading way when ENOMEM is
  returned by finit_module().

  [Regression potential]

  We may introduce a small performance regression when loading multiple
  modules, due to the in-kernel and user-space attempts to load kernel
  modules, however this performance regression is negligible (one
  additional syscall when loading large modules) and it allows to
  correctly support large compressed kernel modules.

  ProblemType: Bug
  DistroRelease: Ubuntu 23.10
  Package: kmod 30+20230519-1ubuntu2
  ProcVersionSignature: User Name 6.5.0-6.6-generic 6.5.0-rc7
  Uname: Linux 6.5.0-6-generic x86_64
  ApportVersion: 2.27.0-0ubuntu2
  Architecture: amd64
  CasperMD5CheckResult: unknown
  CloudArchitecture: x86_64
  CloudBuildName: server
  CloudID: nocloud
  CloudName: unknown
  CloudPlatform: nocloud
  CloudSerial: 20230822
  CloudSubPlatform: config-disk (/dev/vdb)
  Date: Tue Aug 22 15:31:34 2023
  ProcEnviron:
   LANG=C.UTF-8
   PATH=(custom, no user)
   SHELL=/bin/bash
   TERM=xterm-256color
   XDG_RUNTIME_DIR=<set>
  SourcePackage: kmod
  UpgradeStatus: No upgrade log present (probably fresh install)

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