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From:   Ard Biesheuvel <ardb@kernel.org>
Date:   Tue, 21 Nov 2023 11:35:29 -0500
Message-ID: <CAMj1kXH4pWRXWpqUCgWrbBQ9JEQX0MXb5s6+DjL5+_jw0YyLVA@mail.gmail.com>
Subject: Re: [PATCH] arm64: add dependency between vmlinuz.efi and Image
To:     Masahiro Yamada <masahiroy@kernel.org>
Cc:     linux-arm-kernel@lists.infradead.org,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>, linux-kernel@vger.kernel.org,
        linux-kbuild@vger.kernel.org, Simon Glass <sjg@chromium.org>
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On Sun, 19 Nov 2023 at 00:32, Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> A common issue in Makefile is a race in parallel building.
>
> You need to be careful to prevent multiple threads from writing to the
> same file simultaneously.
>
> Commit 3939f3345050 ("ARM: 8418/1: add boot image dependencies to not
> generate invalid images") addressed such a bad scenario.
>
> A similar symptom occurs with the following command:
>
>   $ make -j$(nproc) ARCH=arm64 Image vmlinuz.efi
>     [ snip ]
>     SORTTAB vmlinux
>     OBJCOPY arch/arm64/boot/Image
>     OBJCOPY arch/arm64/boot/Image
>     AS      arch/arm64/boot/zboot-header.o
>     PAD     arch/arm64/boot/vmlinux.bin
>     GZIP    arch/arm64/boot/vmlinuz
>     OBJCOPY arch/arm64/boot/vmlinuz.o
>     LD      arch/arm64/boot/vmlinuz.efi.elf
>     OBJCOPY arch/arm64/boot/vmlinuz.efi
>
> The log "OBJCOPY arch/arm64/boot/Image" is displayed twice.
>
> It indicates that two threads simultaneously enter arch/arm64/boot/
> and write to arch/arm64/boot/Image.
>
> It occasionally leads to a build failure:
>
>   $ make -j$(nproc) ARCH=arm64 Image vmlinuz.efi
>     [ snip ]
>     SORTTAB vmlinux
>     OBJCOPY arch/arm64/boot/Image
>     PAD     arch/arm64/boot/vmlinux.bin
>   truncate: Invalid number: 'arch/arm64/boot/vmlinux.bin'
>   make[2]: *** [drivers/firmware/efi/libstub/Makefile.zboot:13:
>   arch/arm64/boot/vmlinux.bin] Error 1
>   make[2]: *** Deleting file 'arch/arm64/boot/vmlinux.bin'
>   make[1]: *** [arch/arm64/Makefile:163: vmlinuz.efi] Error 2
>   make[1]: *** Waiting for unfinished jobs....
>   make: *** [Makefile:234: __sub-make] Error 2
>
> vmlinuz.efi depends on Image, but such a dependency is not specified
> in arch/arm64/Makefile.
>

To clarify, this dependency /is/ specified in
arch/arm64/boot/Makefile, which is consumed by explicit make
invocations from arch/arm64/Makefile, and these may end up racing with
each other.


> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Acked-by: Ard Biesheuvel <ardb@kernel.org>

> ---
>
>  arch/arm64/Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
> index 4a1ad3248c2d..47ecc4cff9d2 100644
> --- a/arch/arm64/Makefile
> +++ b/arch/arm64/Makefile
> @@ -158,7 +158,7 @@ endif
>
>  all:   $(notdir $(KBUILD_IMAGE))
>
> -
> +vmlinuz.efi: Image
>  Image vmlinuz.efi: vmlinux
>         $(Q)$(MAKE) $(build)=$(boot) $(boot)/$@
>
> --
> 2.40.1
>