selftests: centralise maybe-unused definition in kselftest.h

Several selftests subdirectories duplicated the define __maybe_unused,
leading to redundant code.  Move to kselftest.h header and remove other
definitions.

This addresses the duplication noted in the proc-pid-vm warning fix

Link: https://lkml.kernel.org/r/20250821101159.2238-1-reddybalavignesh9979@gmail.com
Signed-off-by: Bala-Vignesh-Reddy <reddybalavignesh9979@gmail.com>
Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Link:https://lore.kernel.org/lkml/20250820143954.33d95635e504e94df01930d0@linux-foundation.org/
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
Acked-by: SeongJae Park <sj@kernel.org>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Acked-by: Mickal Salan <mic@digikod.net>	[landlock]
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

tools/testing/selftests/kselftest.h

@@ -92,6 +92,10 @@
 #endif
 #define __printf(a, b)   __attribute__((format(printf, a, b)))
 
+#ifndef __maybe_unused
+#define __maybe_unused __attribute__((__unused__))
+#endif
+
 /* counters */
 struct ksft_count {
 	unsigned int ksft_pass;

tools/testing/selftests/landlock/audit.h

@@ -20,14 +20,12 @@
 #include <sys/time.h>
 #include <unistd.h>
 
+#include "../kselftest.h"
+
 #ifndef ARRAY_SIZE
 #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))
 #endif
 
-#ifndef __maybe_unused
-#define __maybe_unused __attribute__((__unused__))
-#endif
-
 #define REGEX_LANDLOCK_PREFIX "^audit([0-9.:]\\+): domain=\\([0-9a-f]\\+\\)"
 
 struct audit_filter {

tools/testing/selftests/landlock/common.h

@@ -22,10 +22,6 @@
 
 #define TMP_DIR "tmp"
 
-#ifndef __maybe_unused
-#define __maybe_unused __attribute__((__unused__))
-#endif
-
 /* TEST_F_FORK() should not be used for new tests. */
 #define TEST_F_FORK(fixture_name, test_name) TEST_F(fixture_name, test_name)
 

tools/testing/selftests/mm/pkey-helpers.h

@@ -84,9 +84,6 @@ extern void abort_hooks(void);
 #ifndef noinline
 # define noinline __attribute__((noinline))
 #endif
-#ifndef __maybe_unused
-# define __maybe_unused __attribute__((__unused__))
-#endif
 
 int sys_pkey_alloc(unsigned long flags, unsigned long init_val);
 int sys_pkey_free(unsigned long pkey);

tools/testing/selftests/net/psock_lib.h

@@ -22,10 +22,6 @@
 
 #define PORT_BASE			8000
 
-#ifndef __maybe_unused
-# define __maybe_unused		__attribute__ ((__unused__))
-#endif
-
 static __maybe_unused void pair_udp_setfilter(int fd)
 {
 	/* the filter below checks for all of the following conditions that

tools/testing/selftests/perf_events/watermark_signal.c

@@ -17,8 +17,6 @@
 
 #include "../kselftest_harness.h"
 
-#define __maybe_unused __attribute__((__unused__))
-
 static int sigio_count;
 
 static void handle_sigio(int signum __maybe_unused,

tools/testing/selftests/ublk/utils.h

@@ -2,8 +2,6 @@
 #ifndef KUBLK_UTILS_H
 #define KUBLK_UTILS_H
 
-#define __maybe_unused __attribute__((unused))
-
 #ifndef min
 #define min(a, b) ((a) < (b) ? (a) : (b))
 #endif