kbuild: Mark the gzip recipes as recursive

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>

Documentation/kbuild/makefiles.rst

@@ -1452,13 +1452,16 @@ objcopy
   OBJCOPYFLAGS_$@ may be used to set additional options.
 
 gzip
-  Compress target. Use maximum compression to compress target.
+  Compress target. Use maximum compression to compress target. Prefix the
+  recipe line with '+' so that GNU Make passes it the jobserver, which
+  scripts/jobserver-exec needs to run pigz (if available) on the free job
+  slots.
 
   Example::
 
     #arch/x86/boot/compressed/Makefile
     $(obj)/vmlinux.bin.gz: $(vmlinux.bin.all-y) FORCE
-            $(call if_changed,gzip)
+            +$(call if_changed,gzip)
 
 dtc
   Create flattened device tree blob object suitable for linking

arch/alpha/boot/Makefile

@@ -40,7 +40,7 @@ endif
 
 # Compressed kernel image
 $(obj)/vmlinux.gz: $(obj)/vmlinux FORCE
-	$(call if_changed,gzip)
+	+$(call if_changed,gzip)
 	@echo '  Kernel $@ is ready'
 
 $(obj)/main.o: $(obj)/ksize.h
@@ -85,7 +85,7 @@ $(obj)/vmlinux.nh: vmlinux $(OBJSTRIP) FORCE
 	$(call if_changed,objstrip)
 
 $(obj)/vmlinux.nh.gz: $(obj)/vmlinux.nh FORCE
-	$(call if_changed,gzip)
+	+$(call if_changed,gzip)
 
 $(obj)/tools/lxboot: $(obj)/bootloader $(OBJSTRIP) FORCE
 	$(call if_changed,objstrip)

arch/arc/boot/Makefile

@@ -23,7 +23,7 @@ $(obj)/vmlinux.bin: vmlinux FORCE
 	$(call if_changed,objcopy)
 
 $(obj)/vmlinux.bin.gz: $(obj)/vmlinux.bin FORCE
-	$(call if_changed,gzip)
+	+$(call if_changed,gzip)
 
 $(obj)/vmlinux.bin.lzma: $(obj)/vmlinux.bin FORCE
 	$(call if_changed,lzma)

arch/arm/boot/compressed/Makefile

@@ -153,7 +153,7 @@ $(obj)/vmlinux: $(obj)/vmlinux.lds $(obj)/$(HEAD) $(obj)/piggy.o \
 	@$(check_for_bad_syms)
 
 $(obj)/piggy_data: $(obj)/../Image FORCE
-	$(call if_changed,$(compress-y))
+	+$(call if_changed,$(compress-y))
 
 $(obj)/piggy.o: $(obj)/piggy_data
 

arch/arm64/boot/Makefile

@@ -26,7 +26,7 @@ $(obj)/Image.bz2: $(obj)/Image FORCE
 	$(call if_changed,bzip2)
 
 $(obj)/Image.gz: $(obj)/Image FORCE
-	$(call if_changed,gzip)
+	+$(call if_changed,gzip)
 
 $(obj)/Image.lz4: $(obj)/Image FORCE
 	$(call if_changed,lz4)

arch/csky/boot/Makefile

@@ -12,7 +12,7 @@ compress-$(CONFIG_KERNEL_XZ)   = xzkern
 compress-$(CONFIG_KERNEL_LZ4)  = lz4
 
 $(obj)/zImage:  $(obj)/Image FORCE
-	$(call if_changed,$(compress-y))
+	+$(call if_changed,$(compress-y))
 	@echo '  Kernel: $@ is ready'
 
 UIMAGE_ARCH		= sandbox

arch/microblaze/boot/Makefile

@@ -14,7 +14,7 @@ $(obj)/linux.bin.ub: $(obj)/linux.bin FORCE
 	$(call if_changed,uimage)
 
 $(obj)/linux.bin.gz: $(obj)/linux.bin FORCE
-	$(call if_changed,gzip)
+	+$(call if_changed,gzip)
 
 quiet_cmd_strip = STRIP   $< $@$2
 	cmd_strip = $(STRIP) -K microblaze_start -K _end -K __log_buf \

arch/mips/boot/Makefile

@@ -63,7 +63,7 @@ $(obj)/vmlinux.bin.bz2: $(obj)/vmlinux.bin FORCE
 	$(call if_changed,bzip2)
 
 $(obj)/vmlinux.bin.gz: $(obj)/vmlinux.bin FORCE
-	$(call if_changed,gzip)
+	+$(call if_changed,gzip)
 
 $(obj)/vmlinux.bin.lzma: $(obj)/vmlinux.bin FORCE
 	$(call if_changed,lzma)

arch/mips/boot/compressed/Makefile

@@ -69,7 +69,7 @@ tool_$(CONFIG_KERNEL_ZSTD)    = zstd22_with_size
 targets += vmlinux.bin.z
 
 $(obj)/vmlinux.bin.z: $(obj)/vmlinux.bin FORCE
-	$(call if_changed,$(tool_y))
+	+$(call if_changed,$(tool_y))
 
 targets += piggy.o dummy.o
 

arch/nios2/boot/Makefile

@@ -18,7 +18,7 @@ $(obj)/vmlinux.bin: vmlinux FORCE
 	$(call if_changed,objcopy)
 
 $(obj)/vmlinux.gz: $(obj)/vmlinux.bin FORCE
-	$(call if_changed,gzip)
+	+$(call if_changed,gzip)
 
 $(obj)/vmImage: $(obj)/vmlinux.gz FORCE
 	$(call if_changed,uimage)

arch/parisc/boot/compressed/Makefile

@@ -55,7 +55,7 @@ suffix-$(CONFIG_KERNEL_LZO)  := lzo
 suffix-$(CONFIG_KERNEL_XZ)  := xz
 
 $(obj)/vmlinux.bin.gz: $(obj)/vmlinux.bin FORCE
-	$(call if_changed,gzip)
+	+$(call if_changed,gzip)
 $(obj)/vmlinux.bin.bz2: $(obj)/vmlinux.bin FORCE
 	$(call if_changed,bzip2_with_size)
 $(obj)/vmlinux.bin.lz4: $(obj)/vmlinux.bin FORCE

arch/riscv/boot/Makefile

@@ -23,7 +23,7 @@ $(obj)/Image: vmlinux FORCE
 	$(call if_changed,objcopy)
 
 $(obj)/Image.gz: $(obj)/Image FORCE
-	$(call if_changed,gzip)
+	+$(call if_changed,gzip)
 
 $(obj)/loader.o: $(src)/loader.S $(obj)/Image
 

arch/s390/boot/Makefile

@@ -117,7 +117,7 @@ suffix-$(CONFIG_KERNEL_XZ)  := .xz
 suffix-$(CONFIG_KERNEL_ZSTD)  := .zst
 
 $(obj)/vmlinux.bin.gz: $(obj)/vmlinux.bin FORCE
-	$(call if_changed,gzip)
+	+$(call if_changed,gzip)
 $(obj)/vmlinux.bin.bz2: $(obj)/vmlinux.bin FORCE
 	$(call if_changed,bzip2_with_size)
 $(obj)/vmlinux.bin.lz4: $(obj)/vmlinux.bin FORCE

arch/sh/boot/Makefile

@@ -66,7 +66,7 @@ $(obj)/vmlinux.bin: vmlinux FORCE
 	$(call if_changed,objcopy)
 
 $(obj)/vmlinux.bin.gz: $(obj)/vmlinux.bin FORCE
-	$(call if_changed,gzip)
+	+$(call if_changed,gzip)
 
 $(obj)/vmlinux.bin.bz2: $(obj)/vmlinux.bin FORCE
 	$(call if_changed,bzip2)

arch/sh/boot/compressed/Makefile

@@ -39,7 +39,7 @@ $(obj)/vmlinux.bin: vmlinux FORCE
 	$(call if_changed,objcopy)
 
 $(obj)/vmlinux.bin.gz: $(obj)/vmlinux.bin FORCE
-	$(call if_changed,gzip)
+	+$(call if_changed,gzip)
 $(obj)/vmlinux.bin.bz2: $(obj)/vmlinux.bin FORCE
 	$(call if_changed,bzip2_with_size)
 $(obj)/vmlinux.bin.lzma: $(obj)/vmlinux.bin FORCE

arch/sparc/boot/Makefile

@@ -23,7 +23,7 @@ ifeq ($(CONFIG_SPARC64),y)
 # Actual linking
 
 $(obj)/zImage: $(obj)/image FORCE
-	$(call if_changed,gzip)
+	+$(call if_changed,gzip)
 	@$(kecho) 'Kernel: $@ is ready' '(#'$(or $(KBUILD_BUILD_VERSION),`cat .version`)')'
 
 $(obj)/vmlinux.aout: vmlinux FORCE
@@ -45,7 +45,7 @@ $(obj)/image.bin: $(obj)/image FORCE
 	$(call if_changed,objcopy)
 
 $(obj)/image.gz: $(obj)/image.bin FORCE
-	$(call if_changed,gzip)
+	+$(call if_changed,gzip)
 
 UIMAGE_LOADADDR = $(CONFIG_UBOOT_LOAD_ADDR)
 UIMAGE_ENTRYADDR = $(CONFIG_UBOOT_ENTRY_ADDR)

arch/x86/boot/compressed/Makefile

@@ -133,7 +133,7 @@ vmlinux.bin.all-y := $(obj)/vmlinux.bin
 vmlinux.bin.all-$(CONFIG_X86_NEED_RELOCS) += $(obj)/vmlinux.relocs
 
 $(obj)/vmlinux.bin.gz: $(vmlinux.bin.all-y) FORCE
-	$(call if_changed,gzip)
+	+$(call if_changed,gzip)
 $(obj)/vmlinux.bin.bz2: $(vmlinux.bin.all-y) FORCE
 	$(call if_changed,bzip2_with_size)
 $(obj)/vmlinux.bin.lzma: $(vmlinux.bin.all-y) FORCE

arch/xtensa/boot/Makefile

@@ -36,7 +36,7 @@ $(obj)/vmlinux.bin: vmlinux FORCE
 	$(call if_changed,objcopy)
 
 $(obj)/vmlinux.bin.gz: $(obj)/vmlinux.bin FORCE
-	$(call if_changed,gzip)
+	+$(call if_changed,gzip)
 
 boot-elf: $(obj)/vmlinux.bin
 boot-redboot: $(obj)/vmlinux.bin.gz

drivers/firmware/efi/libstub/Makefile.zboot

@@ -24,7 +24,7 @@ zboot-method-$(CONFIG_KERNEL_ZSTD)	:= zstd22_with_size
 zboot-size-len-$(CONFIG_KERNEL_ZSTD)	:= 4
 
 $(obj)/vmlinuz: $(obj)/vmlinux.bin FORCE
-	$(call if_changed,$(zboot-method-y))
+	+$(call if_changed,$(zboot-method-y))
 
 # avoid eager evaluation to prevent references to non-existent build artifacts
 OBJCOPYFLAGS_vmlinuz.o = -I binary -O $(EFI_ZBOOT_BFD_TARGET) $(EFI_ZBOOT_OBJCOPY_FLAGS) \

usr/Makefile

@@ -78,7 +78,7 @@ $(obj)/initramfs_data.cpio: $(src)/gen_initramfs.sh $(obj)/gen_init_cpio $(deps_
 endif
 
 $(obj)/initramfs_inc_data: $(cpio-data) FORCE
-	$(call if_changed,$(compress-y))
+	+$(call if_changed,$(compress-y))
 
 targets += initramfs_data.cpio initramfs_inc_data