Re: [PATCH v1 1/2] kbuild: Mark the kernel image gzip recipes as recursive

[Kees Cook <kees@kernel.org>]

On Fri, Oct 09, 2026 at 08:51:18AM -0700, Paul E. McKenney wrote:
> On Thu, Oct 08, 2026 at 11:27:30PM -0700, Kees Cook wrote:
> > Since commit 48ebe1cbbeb51 ("kbuild: compress the kernel with pigz if
> > available"), cmd_gzip runs pigz through scripts/jobserver-exec, which
> > takes the job slots make has free. GNU Make passes the jobserver pipe
> > only to recipes it treats as recursive, but leaves --jobserver-auth in
> > MAKEFLAGS for all of them. The make 4.3 in CentOS Stream 9 also hides
> > the pipe in sub-makes (a backport of the fix for GNU Make bug 58232), so
> > jobserver-exec cannot open it, runs pigz on one thread, and prints:
> > 
> >   WARNING: Unable to reopen jobserver read-side pipe: FileNotFoundError(2, 'No such file or directory')
> > 
> > Mark the gzip recipes as recursive with "+", as commit ecab4115c44cc
> > ("kbuild: mark `rustc` (and others) invocations as recursive") did for
> > rustc. As with those, "make -n" now runs them.
> > 
> > Tested ARCH=x86_64 and ARCH=arm64 defconfig with GNU Make 4.3 plus
> > CentOS Stream 9's make-4.3-cloexec.patch, GCC 16.2.0, and -j64: without
> > this change the warning appears and pigz runs with "-p 1"; with it there
> > is no warning, and pigz runs with "-p 54" and "-p 64".
> 
> Thank you, Kees!
> 
> My initial test of this patch (using rcutorture) still showed the failure.

Oh! So the patch didn't fix it for you?

> I am running GCC 11.5.0 and without any patches to "make".  I take it
> that I need to find and apply CentOS Stream 9's make-4.3-cloexec.patch?
> 
> But if I use "make -j" instead of rcutorture, this patch does work fine.
> Even with "make -j632".

Without rcutorture was "make -jNN" broken for you without this patch?

> I put rcutorture in the background using nohup and full redirection,
> but "nohup make -j632 > /tmp/Make.out 2>&1 < /dev/null &" works just
> fine.  And running rcutorture in the foreground still fails.
> 
> Very strange.

O_O It only breaks ... when backgrounded? Oh my. Okay, I will try to
figure that out.

-- 
Kees Cook