openafs-modules-dkms: build failure on hirsute with kernel 5.11

[Andrea Righi]

[Impact]

Linux 5.11 removed TIF_IA32 with commit 8d71d2bf6efec ("x86: Reclaim TIF_IA32 and TIF_X32"), this flag is used by openafs to determine if the task is handling a syscall request from a 32 bit process, so building against a 5.11 kernel results in a build failure.

[Test case]

Install openafs-modules-dkms.

[Fix]

Apply the following openafs' upstream commits:

  32cc6b0796495e596262d84c428172a511f757c4 ("Linux: Refactor test for 32bit compat")
  78ef922612bef5f5fd6904896e84b9d2ea802404 ("Linux 5.11: Test 32bit compat with in_compat_syscall")

In this way we are not relying anymore on TIF_IA32 and instead we use the function in_compat_syscall() introdueed in Linux 4.6, as a preferred method to determine if a syscall needs to handle a compatible call (e.g., 32-bit binaries).

[Regression potential]

This change might break the build of kernels that are missing in_compat_syscall(), but this is unlikely to happen with recent kernels, since this function has been introduced in Linux 4.6 (and it's available on all architectures).

[Andrea Righi (arighi)]

openafs builds correctly with the attached debdiff.

[Launchpad Janitor (janitor)]

This bug was fixed in the package openafs - 1.8.6-5ubuntu1

---------------
openafs (1.8.6-5ubuntu1) hirsute; urgency=medium

  * Support linux 5.11 (LP: #1915854):
    - debian/patches/0020-Linux-Refactor-test-for-32bit-compat.patch
    - debian/patches/0021-Linux-5.11-Test-32bit-compat-with-in_compat_syscall.patch

 -- Andrea Righi <email address hidden> Tue, 16 Feb 2021 17:12:48 +0000

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.