linux-kernel - Cannot parse struct or union error on mm-everything

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Message-ID: <Y3hXJ0D+qAwfpm7B@debian.me>
Date:   Sat, 19 Nov 2022 11:10:15 +0700
From:   Bagas Sanjaya <bagasdotme@...il.com>
To:     Linux Documentation <linux-doc@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        David Hildenbrand <david@...hat.com>,
        Hugh Dickins <hughd@...gle.com>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Peter Xu <peterx@...hat.com>, Yu Zhao <yuzhao@...gle.com>,
        Colin Cross <ccross@...gle.com>, Arnd Bergmann <arnd@...db.de>,
        Pasha Tatashin <pasha.tatashin@...een.com>
Subject: Cannot parse struct or union error on mm-everything

Greetings,

I found a new htmldocs warning on mm-everything:

WARNING: kernel-doc './scripts/kernel-doc -rst -enable-lineno -sphinx-version 2.4.4 -internal ./include/linux/mm_types.h' failed with return code 1

Checking the header with './scripts/kernel-doc -v -none 
./include/linux/mm_types.h', I got the full error:

include/linux/mm_types.h:255: info: Scanning doc for struct encoded_page
include/linux/mm_types.h:268: error: Cannot parse struct or union!
include/linux/mm_types.h:287: info: Scanning doc for struct folio
include/linux/mm_types.h:917: info: Scanning doc for typedef vm_fault_t
include/linux/mm_types.h:924: info: Scanning doc for enum vm_fault_reason
include/linux/mm_types.h:1028: info: Scanning doc for enum fault_flag
1 errors

The culprit is encoded_page struct, which is null struct (nonexistent type)
with kernel-doc comments:

/**
 * struct encoded_page - a nonexistent type marking this pointer
 *
 * An 'encoded_page' pointer is a pointer to a regular 'struct page', but
 * with the low bits of the pointer indicating extra context-dependent
 * information. Not super-common, but happens in mmu_gather and mlock
 * handling, and this acts as a type system check on that use.
 *
 * We only really have two guaranteed bits in general, although you could
 * play with 'struct page' alignment (see CONFIG_HAVE_ALIGNED_STRUCT_PAGE)
 * for more.
 *
 * Use the supplied helper functions to endcode/decode the pointer and bits.
 */
struct encoded_page;

The struct is introduced by d57ab372568585 ("mm: introduce 'encoded' page
pointers with embedded extra bits").

Thanks.

-- 
An old man doll... just what I always wanted! - Clara

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