linux-kernel - [PATCH] mm/memremap: Mark folio_span_valid() as __maybe

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Date:   Tue, 18 Oct 2022 08:26:46 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Dan Williams <dan.j.williams@...el.com>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        patches@...ts.linux.dev, Nathan Chancellor <nathan@...nel.org>
Subject: [PATCH] mm/memremap: Mark folio_span_valid() as __maybe_unused

When building without CONFIG_DEBUG_VM, clang warns:

  mm/memremap.c:495:13: error: function 'folio_span_valid' is not needed and will not be emitted [-Werror,-Wunneeded-internal-declaration]
  static bool folio_span_valid(struct dev_pagemap *pgmap, struct folio *folio,
              ^
  1 error generated.

folio_span_valid() is only used within a instance of VM_WARN_ON_ONCE(),
which evaluates to BUILD_BUG_ON_INVALID() with CONFIG_DEBUG_VM=n, which
ultimately resolves to sizeof(), which is fully resolved at compile
time. Basically, the warning is flagging that folio_span_valid() is
only used in a compile time context and will not be called at run time.

Since this is expected given the configuration, mark folio_span_valid()
as __maybe_unused so that there is no warning.

Fixes: 07108d5bfeeb ("fsdax: introduce pgmap_request_folios()")
Link: https://github.com/ClangBuiltLinux/linux/issues/1739
Signed-off-by: Nathan Chancellor <nathan@...nel.org>
---

I am aware the Fixes SHA is probably not stable but I figured I would
include it anyways.

 mm/memremap.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/memremap.c b/mm/memremap.c
index 53fe30bb79bb..02b796749b72 100644
--- a/mm/memremap.c
+++ b/mm/memremap.c
@@ -492,8 +492,9 @@ void free_zone_device_page(struct page *page)
 	put_dev_pagemap(page->pgmap);
 }
 
-static bool folio_span_valid(struct dev_pagemap *pgmap, struct folio *folio,
-			     int nr_folios)
+static __maybe_unused bool folio_span_valid(struct dev_pagemap *pgmap,
+					    struct folio *folio,
+					    int nr_folios)
 {
 	unsigned long pfn_start, pfn_end;
 

base-commit: f5938bbbb79d48ca167e305c228dccbecea0309e
-- 
2.38.0