Re: Odd build breakage in 4.9-rc7

[Prarit Bhargava]

On 11/30/2016 05:41 PM, Nicolas Pitre wrote:
> On Wed, 30 Nov 2016, Linus Torvalds wrote:
> 
>> On Wed, Nov 30, 2016 at 10:50 AM, Prarit Bhargava <prarit@xxxxxxxxxx> wrote:
>>>
>>> It comes back.  The steps to reproduce this are:
>>>
>>> 1.  checkout latest linux.git
>>> 2.  make -j112
>>>
>>> (IOW, it occurs 100% of the time for me on a clean tree.)
> 
> I don't have access to such hardware where -j112 could ever make sense.  :-)
> In other words, I can't reproduce regardless of the -j value I try.
> 
>> I suspect it's not new, it's just that you are able to hit the timing
>> just right (and the new include presumable makes that just be much
>> easier).
> 
> Here's the best fix I can think of. I can't convince myself any other 
> location would be 100% safe.  Obviously I can't confirm if this actually 
> fixes anything.
> 
> ----- >8
> Subject: kbuild: make sure autoksyms.h exists early
> 
> Some people are able to trigger a race where autoksyms.h is used before
> its empty version is even created. Let's create it at the same time as
> the directory holding it is created.
> 
> Signed-off-by: Nicolas Pitre <nico@xxxxxxxxxx>
> 
> diff --git a/Makefile b/Makefile
> index 694111b43c..9f9c3b577c 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1019,8 +1019,6 @@ prepare2: prepare3 prepare-compiler-check outputmakefile asm-generic
>  prepare1: prepare2 $(version_h) include/generated/utsrelease.h \
>                     include/config/auto.conf
>  	$(cmd_crmodverdir)
> -	$(Q)test -e include/generated/autoksyms.h || \
> -	    touch   include/generated/autoksyms.h
>  
>  archprepare: archheaders archscripts prepare1 scripts_basic
>  
> diff --git a/scripts/kconfig/Makefile b/scripts/kconfig/Makefile
> index ebced77deb..90a091b6ae 100644
> --- a/scripts/kconfig/Makefile
> +++ b/scripts/kconfig/Makefile
> @@ -35,6 +35,8 @@ nconfig: $(obj)/nconf
>  
>  silentoldconfig: $(obj)/conf
>  	$(Q)mkdir -p include/config include/generated
> +	$(Q)test -e include/generated/autoksyms.h || \
> +	    touch   include/generated/autoksyms.h
>  	$< $(silent) --$@ $(Kconfig)
>  
>  localyesconfig localmodconfig: $(obj)/streamline_config.pl $(obj)/conf
> 

The testing was successful.

After testing an hour of builds with different -j values, I'm no longer seeing
any compile issues when this patch is applied.  When I remove the patch the
compile error returns so I'm going to say that this patch fixed it.

Thanks again Nicolas.

Tested-by: Prarit Bhargava <prarit@xxxxxxxxxx>

P.