[Bug 2122419] Re: lttng-modules FTBFS in Questing with kernel 6.17

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** Tags added: patch

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https://bugs.launchpad.net/bugs/2122419

Title:
  lttng-modules FTBFS in Questing with kernel 6.17

Status in lttng-modules package in Ubuntu:
  In Progress
Status in lttng-modules source package in Questing:
  In Progress

Bug description:
  [ Impact ]

  lttng-modules does not compile from source in Questing with kernel
  6.17:

  src/../include/ringbuffer/frontend_api.h: In function ‘lib_ring_buffer_reserve’:
  /usr/src/linux-headers-6.17.0-3-generic/include/linux/percpu-defs.h:220:45: error: initialization from pointer to non-enclosed address space
    220 |         const void __percpu *__vpp_verify = (typeof((ptr) + 0))NULL;    \
        |                                             ^
  /usr/src/linux-headers-6.17.0-3-generic/include/linux/percpu-defs.h:238:9: note: in expansion of macro ‘__verify_pcpu_ptr’
    238 |         __verify_pcpu_ptr(ptr);                                         \
        |         ^~~~~~~~~~~~~~~~~
  src/../include/ringbuffer/frontend_api.h:155:23: note: in expansion of macro ‘per_cpu_ptr’
    155 |                 buf = per_cpu_ptr(chan->backend.buf, ctx->priv.reserve_cpu);
        |                       ^~~~~~~~~~~

  [ Fix ]

  Patch the code to properly support Linux 6.17 by applying the following commits from upstream:
  - f86e2417 fix: percpu: repurpose __percpu tag as a named address space qualifier (v6.15)
  - 49403039 fix: mm: remove the for_reclaim field from struct writeback_control (v6.17)

  [ Test Plan ]

  Build the dkms correctly on Questing:

  $ sudo apt install -y lttng-modules-dkms
  $ dkms status
  lttng-modules/2.14.0, 6.17.0-3-generic, x86_64: installed

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