Re: Odd build breakage in 4.9-rc7

[Jarod Wilson]

On 2016-12-01 9:03 AM, Prarit Bhargava wrote:
> 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>

Looks good here as well, can do parallel make w/o reverting Tony's 
patches again.

Tested-by: Jarod Wilson <jarod@xxxxxxxxxx>

--
Jarod Wilson
jarod@xxxxxxxxxx