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

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[ 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

** Affects: lttng-modules (Ubuntu)
     Importance: Undecided
     Assignee: Massimiliano Pellizzer (mpellizzer)
         Status: In Progress

** Affects: lttng-modules (Ubuntu Questing)
     Importance: Undecided
     Assignee: Massimiliano Pellizzer (mpellizzer)
         Status: In Progress


** Tags: patch
-- 
lttng-modules FTBFS in Questing with kernel 6.17
https://bugs.launchpad.net/bugs/2122419
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