Since commit 48ebe1cbbe ("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 every recipe that can run cmd_gzip as recursive with "+", as
commit ecab4115c4 ("kbuild: mark `rustc` (and others) invocations as
recursive") did for rustc. Besides the $(call if_changed,gzip) rules,
this covers those that choose gzip through a variable: the built-in
initramfs in usr/Makefile (which rcutorture's kvm.sh builds), the EFI
zboot image, and the arm, csky, and mips compressed images. As with
rustc, "make -n" now runs these recipes, including those that choose
through a variable when they select another compressor. Also update the
gzip entry in Documentation/kbuild/makefiles.rst, as suggested in
review.
Tested with GNU Make 4.3 plus CentOS Stream 9's make-4.3-cloexec.patch,
GCC 16.2.0, and -j64, on ARCH=x86_64, arm64, and arm defconfig, and
ARCH=x86_64 defconfig with a built-in initramfs: none of them prints the
warning, and pigz gets the free job slots (-p 54, 64, and 50 for the
kernel image). Without this change, the x86_64 builds print it for the
kernel image and for the initramfs.
Reported-by: Paul E. McKenney <paulmck@kernel.org>
Closes: https://lore.kernel.org/all/0ddb5e5e-f801-444c-aa98-0cfe814a3026@paulmck-laptop/
Fixes: 48ebe1cbbe ("kbuild: compress the kernel with pigz if available")
Assisted-by: LLM
Reviewed-by: Nicolas Schier <n.schier@fritz.com>
Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Signed-off-by: Kees Cook <kees@kernel.org>
Tested-by: Paul E. McKenney <paulmck@kernel.org>
Link: https://patch.msgid.link/20261010081914.540611-1-kees@kernel.org
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
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