selftests/mm: build with -O2

commit 4603618 upstream.

The mm kselftests are currently built with no optimisation (-O0).  It's
unclear why, and besides being obviously suboptimal, this also prevents
the pkeys tests from working as intended.  Let's build all the tests with
-O2.

[[email protected]: silence unused-result warnings]
  Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Kevin Brodsky <[email protected]>
Cc: Aruna Ramakrishna <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Joey Gouly <[email protected]>
Cc: Keith Lucas <[email protected]>
Cc: Ryan Roberts <[email protected]>
Cc: Shuah Khan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
[ Yifei: This commit also fix the failure of pkey_sighandler_tests_64,
  which is also in linux-6.12.y, thus backport this commit. ]
Signed-off-by: Yifei Liu <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: kevin-brodsky-arm

tools/testing/selftests/mm/Makefile

@@ -33,9 +33,16 @@ endif
 # LDLIBS.
 MAKEFLAGS += --no-builtin-rules
 
-CFLAGS = -Wall -I $(top_srcdir) $(EXTRA_CFLAGS) $(KHDR_INCLUDES) $(TOOLS_INCLUDES)
+CFLAGS = -Wall -O2 -I $(top_srcdir) $(EXTRA_CFLAGS) $(KHDR_INCLUDES) $(TOOLS_INCLUDES)
 LDLIBS = -lrt -lpthread -lm
 
+# Some distributions (such as Ubuntu) configure GCC so that _FORTIFY_SOURCE is
+# automatically enabled at -O1 or above. This triggers various unused-result
+# warnings where functions such as read() or write() are called and their
+# return value is not checked. Disable _FORTIFY_SOURCE to silence those
+# warnings.
+CFLAGS += -U_FORTIFY_SOURCE
+
 TEST_GEN_FILES = cow
 TEST_GEN_FILES += compaction_test
 TEST_GEN_FILES += gup_longterm