selftests: Preserve subtarget failures in all/install

Track failures explicitly in the top-level selftests all/install loops.

The current code multiplies `ret` by each sub-make exit status. For
example, with `TARGETS=net`, the implicit `net/lib` dependency runs after
`net`, so a failed `net` build can be followed by a successful `net/lib`
build and reset the final result to success.

Set `ret` to 1 on any non-zero sub-make exit code and keep it sticky, so
the top-level make returns failure when any selected selftest target
fails.

Signed-off-by: Ricardo B. Marlière <rbm@suse.com>
Link: https://lore.kernel.org/r/20260320-selftests-fixes-v1-5-79144f76be01@suse.com
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

Author: rbmarliere

tools/testing/selftests/Makefile

@@ -209,14 +209,14 @@ export KHDR_INCLUDES
 .DEFAULT_GOAL := all
 
 all:
-	@ret=1;							\
+	@ret=0;							\
 	for TARGET in $(TARGETS) $(INSTALL_DEP_TARGETS); do	\
 		BUILD_TARGET=$$BUILD/$$TARGET;			\
 		mkdir $$BUILD_TARGET  -p;			\
 		$(MAKE) OUTPUT=$$BUILD_TARGET -C $$TARGET	\
 				O=$(abs_objtree)		\
 				$(if $(FORCE_TARGETS),|| exit);	\
-		ret=$$((ret * $$?));				\
+		[ $$? -eq 0 ] || ret=1;			\
 	done; exit $$ret;
 
 run_tests: all
@@ -274,7 +274,7 @@ ifdef INSTALL_PATH
 	install -m 744 kselftest/ksft.py $(INSTALL_PATH)/kselftest/
 	install -m 744 run_kselftest.sh $(INSTALL_PATH)/
 	rm -f $(TEST_LIST)
-	@ret=1;	\
+	@ret=0;	\
 	for TARGET in $(TARGETS) $(INSTALL_DEP_TARGETS); do \
 		BUILD_TARGET=$$BUILD/$$TARGET;	\
 		$(MAKE) OUTPUT=$$BUILD_TARGET -C $$TARGET install \
@@ -283,7 +283,7 @@ ifdef INSTALL_PATH
 				OBJ_PATH=$(INSTALL_PATH) \
 				O=$(abs_objtree)		\
 				$(if $(FORCE_TARGETS),|| exit);	\
-		ret=$$((ret * $$?));		\
+		[ $$? -eq 0 ] || ret=1;		\
 	done; exit $$ret;