linux-kernel - Re: [PATCH v2] asm-generic: fix variable 'p4d' set but not used

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Date:   Thu, 15 Aug 2019 10:38:33 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Qian Cai <cai@....pw>
Cc:     akpm@...ux-foundation.org, arnd@...db.de,
        kirill.shutemov@...ux.intel.com, mhocko@...e.com, jgg@...pe.ca,
        linux-mm@...ck.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2] asm-generic: fix variable 'p4d' set but not used

On Tue, Aug 06, 2019 at 07:29:17PM -0400, Qian Cai wrote:
> A compiler throws a warning on an arm64 system since the
> commit 9849a5697d3d ("arch, mm: convert all architectures to use
> 5level-fixup.h"),
> 
> mm/kasan/init.c: In function 'kasan_free_p4d':
> mm/kasan/init.c:344:9: warning: variable 'p4d' set but not used
> [-Wunused-but-set-variable]
>  p4d_t *p4d;
>         ^~~
> 
> because p4d_none() in "5level-fixup.h" is compiled away while it is a
> static inline function in "pgtable-nopud.h". However, if converted
> p4d_none() to a static inline there, powerpc would be unhappy as it
> reads those in assembler language in
> "arch/powerpc/include/asm/book3s/64/pgtable.h", so it needs to skip
> assembly include for the static inline C function. While at it,
> converted a few similar functions to be consistent with the ones in
> "pgtable-nopud.h".
> 
> Signed-off-by: Qian Cai <cai@....pw>
> Acked-by: Arnd Bergmann <arnd@...db.de>

All parisc builds fail with this patch applied.

include/asm-generic/5level-fixup.h:14:18: error:
	unknown type name 'pgd_t'; did you mean 'pid_t'?

Bisect results below.

Guenter

---
# bad: [329120423947e8b36fd2f8b5cf69944405d0aece] Merge tag 'auxdisplay-for-linus-v5.3-rc5' of git://github.com/ojeda/linux
# good: [ee1c7bd33e66376067fd6306b730789ee2ae53e4] Merge tag 'tpmdd-next-20190813' of git://git.infradead.org/users/jjs/linux-tpmdd
git bisect start 'HEAD' 'ee1c7bd33e66'
# bad: [e83b009c5c366b678c7986fa6c1d38fed06c954c] Merge tag 'dma-mapping-5.3-4' of git://git.infradead.org/users/hch/dma-mapping
git bisect bad e83b009c5c366b678c7986fa6c1d38fed06c954c
# bad: [92717d429b38e4f9f934eed7e605cc42858f1839] Revert "Revert "mm, thp: consolidate THP gfp handling into alloc_hugepage_direct_gfpmask""
git bisect bad 92717d429b38e4f9f934eed7e605cc42858f1839
# good: [b997052bc3ac444a0bceab1093aff7ae71ed419e] mm/z3fold.c: fix z3fold_destroy_pool() race condition
git bisect good b997052bc3ac444a0bceab1093aff7ae71ed419e
# good: [951531691c4bcaa59f56a316e018bc2ff1ddf855] mm/usercopy: use memory range to be accessed for wraparound check
git bisect good 951531691c4bcaa59f56a316e018bc2ff1ddf855
# good: [6a2aeab59e97101b4001bac84388fc49a992f87e] seq_file: fix problem when seeking mid-record
git bisect good 6a2aeab59e97101b4001bac84388fc49a992f87e
# bad: [0cfaee2af3a04c0be5f056cebe5f804dedc59a43] include/asm-generic/5level-fixup.h: fix variable 'p4d' set but not used
git bisect bad 0cfaee2af3a04c0be5f056cebe5f804dedc59a43
# first bad commit: [0cfaee2af3a04c0be5f056cebe5f804dedc59a43] include/asm-generic/5level-fixup.h: fix variable 'p4d' set but not used