docs: kdoc_parser: add data/function attributes to ignore

Recognize and ignore __rcu (in struct members), __private (in struct
members), and __always_unused (in function parameters) to prevent
kernel-doc warnings:

  Warning: include/linux/rethook.h:38 struct member 'void (__rcu *handler' not described in 'rethook'
  Warning: include/linux/hrtimer_types.h:47 Invalid param: enum hrtimer_restart (*__private function)(struct hrtimer *)
  Warning: security/ipe/hooks.c:81 function parameter '__always_unused' not described in 'ipe_mmap_file'
  Warning: security/ipe/hooks.c:109 function parameter '__always_unused' not described in 'ipe_file_mprotect'

There are more of these (in compiler_types.h, compiler_attributes.h)
that can be added as needed.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <20251127063117.150384-1-rdunlap@infradead.org>

Author: rddunlap

tools/lib/python/kdoc/kdoc_parser.py

@@ -86,6 +86,8 @@
     (KernRe(r'\s*__counted_by_(le|be)\s*\([^;]*\)', re.S), ' '),
     (KernRe(r'\s*__packed\s*', re.S), ' '),
     (KernRe(r'\s*CRYPTO_MINALIGN_ATTR', re.S), ' '),
+    (KernRe(r'\s*__private', re.S), ' '),
+    (KernRe(r'\s*__rcu', re.S), ' '),
     (KernRe(r'\s*____cacheline_aligned_in_smp', re.S), ' '),
     (KernRe(r'\s*____cacheline_aligned', re.S), ' '),
     (KernRe(r'\s*__cacheline_group_(begin|end)\([^\)]+\);'), ''),
@@ -183,6 +185,7 @@
     (KernRe(r"__weak +"), ""),
     (KernRe(r"__sched +"), ""),
     (KernRe(r"_noprof"), ""),
+    (KernRe(r"__always_unused *"), ""),
     (KernRe(r"__printf\s*\(\s*\d*\s*,\s*\d*\s*\) +"), ""),
     (KernRe(r"__(?:re)?alloc_size\s*\(\s*\d+\s*(?:,\s*\d+\s*)?\) +"), ""),
     (KernRe(r"__diagnose_as\s*\(\s*\S+\s*(?:,\s*\d+\s*)*\) +"), ""),