linux-kernel - Re: [PATCH 1/3] um: fix parallel building with O= option

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Date:   Sat, 4 Aug 2018 13:51:56 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>
Cc:     Jeff Dike <jdike@...toit.com>, Richard Weinberger <richard@....at>,
        linux-um@...ts.infradead.org, Randy Dunlap <rdunlap@...radead.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Sam Ravnborg <sam@...nborg.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] um: fix parallel building with O= option

2018-08-04 13:47 GMT+09:00 Masahiro Yamada <yamada.masahiro@...ionext.com>:
> Randy Dunlap reports UML occasionally fails to build with -j<N> and
> O=<builddir> options.
>
>   make[1]: Entering directory '/home/rdunlap/mmotm-2018-0802-1529/UM64'
>     UPD     include/generated/uapi/linux/version.h
>     WRAP    arch/x86/include/generated/asm/dma-contiguous.h
>     WRAP    arch/x86/include/generated/asm/export.h
>     WRAP    arch/x86/include/generated/asm/early_ioremap.h
>     WRAP    arch/x86/include/generated/asm/mcs_spinlock.h
>     WRAP    arch/x86/include/generated/asm/mm-arch-hooks.h
>     WRAP    arch/x86/include/generated/uapi/asm/bpf_perf_event.h
>     WRAP    arch/x86/include/generated/uapi/asm/poll.h
>     GEN     ./Makefile
>   make[2]: *** No rule to make target 'archheaders'.  Stop.
>   arch/um/Makefile:119: recipe for target 'archheaders' failed
>   make[1]: *** [archheaders] Error 2
>   make[1]: *** Waiting for unfinished jobs....
>     UPD     include/config/kernel.release
>   make[1]: *** wait: No child processes.  Stop.
>   Makefile:146: recipe for target 'sub-make' failed
>   make: *** [sub-make] Error 2
>
> The cause of the problem is the use of '$(MAKE) KBUILD_SRC=',
> which recurses to the top Makefile via the $(objtree)/Makefile
> generated by scripts/mkmakefile.
>
> When you run "make -j<N> O=<builddir> ARCH=um", Make can execute
> 'archheaders' and 'outputmakefile' targets simultaneously because
> there is no dependency between them.
>
> If it happens,
>
>   $(Q)$(MAKE) KBUILD_SRC= ARCH=$(HEADER_ARCH) archheaders
>
> ... tries to run $(objtree)/Makefile that is being updated.
>
> The correct way for the recursion is
>
>   $(Q)$(MAKE) -f $(srctree)/Makefile ARCH=$(HEADER_ARCH) archheaders
>
> ..., which does not rely on the generated Makefile.
>



I forgot to add this:

Reported-by: Randy Dunlap <rdunlap@...radead.org>




> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
> ---
>
>  arch/um/Makefile | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/arch/um/Makefile b/arch/um/Makefile
> index e54dda8..de340e4 100644
> --- a/arch/um/Makefile
> +++ b/arch/um/Makefile
> @@ -122,8 +122,7 @@ archheaders:
>         $(Q)$(MAKE) -f $(srctree)/scripts/Makefile.asm-generic \
>                     kbuild-file=$(HOST_DIR)/include/uapi/asm/Kbuild \
>                     obj=$(HOST_DIR)/include/generated/uapi/asm
> -       $(Q)$(MAKE) KBUILD_SRC= ARCH=$(HEADER_ARCH) archheaders
> -
> +       $(Q)$(MAKE) -f $(srctree)/Makefile ARCH=$(HEADER_ARCH) archheaders
>
>  archprepare: include/generated/user_constants.h
>
> --
> 2.7.4
>
> --
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-- 
Best Regards
Masahiro Yamada