4.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx> [ Upstream commit 13d3d01e26b942ada7cfced68ccb6db49597874a ] Randy Dunlap reports UML occasionally fails to build with -j<N> and O=<builddir> options. make[1]: Entering directory '/home/rdunlap/mmotm-2018-0802-1529/UM64' UPD include/generated/uapi/linux/version.h WRAP arch/x86/include/generated/asm/dma-contiguous.h WRAP arch/x86/include/generated/asm/export.h WRAP arch/x86/include/generated/asm/early_ioremap.h WRAP arch/x86/include/generated/asm/mcs_spinlock.h WRAP arch/x86/include/generated/asm/mm-arch-hooks.h WRAP arch/x86/include/generated/uapi/asm/bpf_perf_event.h WRAP arch/x86/include/generated/uapi/asm/poll.h GEN ./Makefile make[2]: *** No rule to make target 'archheaders'. Stop. arch/um/Makefile:119: recipe for target 'archheaders' failed make[1]: *** [archheaders] Error 2 make[1]: *** Waiting for unfinished jobs.... UPD include/config/kernel.release make[1]: *** wait: No child processes. Stop. Makefile:146: recipe for target 'sub-make' failed make: *** [sub-make] Error 2 The cause of the problem is the use of '$(MAKE) KBUILD_SRC=', which recurses to the top Makefile via the $(objtree)/Makefile generated by scripts/mkmakefile. When you run "make -j<N> O=<builddir> ARCH=um", Make can execute 'archheaders' and 'outputmakefile' targets simultaneously because there is no dependency between them. If it happens, $(Q)$(MAKE) KBUILD_SRC= ARCH=$(HEADER_ARCH) archheaders ... tries to run $(objtree)/Makefile that is being updated. The correct way for the recursion is $(Q)$(MAKE) -f $(srctree)/Makefile ARCH=$(HEADER_ARCH) archheaders ..., which does not rely on the generated Makefile. Reported-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx> Signed-off-by: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx> Tested-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx> Acked-by: Richard Weinberger <richard@xxxxxx> Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/um/Makefile | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) --- a/arch/um/Makefile +++ b/arch/um/Makefile @@ -122,8 +122,7 @@ archheaders: $(Q)$(MAKE) -f $(srctree)/scripts/Makefile.asm-generic \ kbuild-file=$(HOST_DIR)/include/uapi/asm/Kbuild \ obj=$(HOST_DIR)/include/generated/uapi/asm - $(Q)$(MAKE) KBUILD_SRC= ARCH=$(HEADER_ARCH) archheaders - + $(Q)$(MAKE) -f $(srctree)/Makefile ARCH=$(HEADER_ARCH) archheaders archprepare: include/generated/user_constants.h