Misc timer fixes:

- Address a (valid) W=1 build warning
 
  - Fix timer self-tests
 
  - Annotate a KCSAN warning wrt. accesses to the
    tick_do_timer_cpu global variable.
 
  - Address a !CONFIG_BUG build warning
 
 Heads up for the !CONFIG_BUG warning patch, which we
 addressed with:
 
    5284984a4f bug: Fix no-return-statement warning with !CONFIG_BUG
 
 Not everyone agreed though, see:
 
   https://lore.kernel.org/all/20240410153212.127477-1-adrian.hunter@intel.com
 
 Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'timers-urgent-2024-04-14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull timer fixes from Ingo Molnar:

 - Address a (valid) W=1 build warning

 - Fix timer self-tests

 - Annotate a KCSAN warning wrt. accesses to the tick_do_timer_cpu
   global variable

 - Address a !CONFIG_BUG build warning

* tag 'timers-urgent-2024-04-14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  selftests: kselftest: Fix build failure with NOLIBC
  selftests: timers: Fix abs() warning in posix_timers test
  selftests: kselftest: Mark functions that unconditionally call exit() as __noreturn
  selftests: timers: Fix posix_timers ksft_print_msg() warning
  selftests: timers: Fix valid-adjtimex signed left-shift undefined behavior
  bug: Fix no-return-statement warning with !CONFIG_BUG
  timekeeping: Use READ/WRITE_ONCE() for tick_do_timer_cpu
  selftests/timers/posix_timers: Reimplement check_timer_distribution()
  irqflags: Explicitly ignore lockdep_hrtimer_exit() argument

include/asm-generic/bug.h

@@ -156,7 +156,10 @@ extern __printf(1, 2) void __warn_printk(const char *fmt, ...);
 
 #else /* !CONFIG_BUG */
 #ifndef HAVE_ARCH_BUG
-#define BUG() do {} while (1)
+#define BUG() do {		\
+	do {} while (1);	\
+	unreachable();		\
+} while (0)
 #endif
 
 #ifndef HAVE_ARCH_BUG_ON

include/linux/irqflags.h

@@ -114,7 +114,7 @@ do {						\
 # define lockdep_softirq_enter()		do { } while (0)
 # define lockdep_softirq_exit()			do { } while (0)
 # define lockdep_hrtimer_enter(__hrtimer)	false
-# define lockdep_hrtimer_exit(__context)	do { } while (0)
+# define lockdep_hrtimer_exit(__context)	do { (void)(__context); } while (0)
 # define lockdep_posixtimer_enter()		do { } while (0)
 # define lockdep_posixtimer_exit()		do { } while (0)
 # define lockdep_irq_work_enter(__work)		do { } while (0)

kernel/time/tick-common.c

@@ -7,6 +7,7 @@
  * Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar
  * Copyright(C) 2006-2007, Timesys Corp., Thomas Gleixner
  */
+#include <linux/compiler.h>
 #include <linux/cpu.h>
 #include <linux/err.h>
 #include <linux/hrtimer.h>
@@ -84,7 +85,7 @@ int tick_is_oneshot_available(void)
  */
 static void tick_periodic(int cpu)
 {
-	if (tick_do_timer_cpu == cpu) {
+	if (READ_ONCE(tick_do_timer_cpu) == cpu) {
 		raw_spin_lock(&jiffies_lock);
 		write_seqcount_begin(&jiffies_seq);
 
@@ -215,8 +216,8 @@ static void tick_setup_device(struct tick_device *td,
 		 * If no cpu took the do_timer update, assign it to
 		 * this cpu:
 		 */
-		if (tick_do_timer_cpu == TICK_DO_TIMER_BOOT) {
+		if (READ_ONCE(tick_do_timer_cpu) == TICK_DO_TIMER_BOOT) {
-			tick_do_timer_cpu = cpu;
+			WRITE_ONCE(tick_do_timer_cpu, cpu);
 			tick_next_period = ktime_get();
 #ifdef CONFIG_NO_HZ_FULL
 			/*
@@ -232,7 +233,7 @@ static void tick_setup_device(struct tick_device *td,
 						!tick_nohz_full_cpu(cpu)) {
 			tick_take_do_timer_from_boot();
 			tick_do_timer_boot_cpu = -1;
-			WARN_ON(tick_do_timer_cpu != cpu);
+			WARN_ON(READ_ONCE(tick_do_timer_cpu) != cpu);
 #endif
 		}
 
@@ -406,10 +407,10 @@ void tick_assert_timekeeping_handover(void)
 int tick_cpu_dying(unsigned int dying_cpu)
 {
 	/*
-	 * If the current CPU is the timekeeper, it's the only one that
+	 * If the current CPU is the timekeeper, it's the only one that can
-	 * can safely hand over its duty. Also all online CPUs are in
+	 * safely hand over its duty. Also all online CPUs are in stop
-	 * stop machine, guaranteed not to be idle, therefore it's safe
+	 * machine, guaranteed not to be idle, therefore there is no
-	 * to pick any online successor.
+	 * concurrency and it's safe to pick any online successor.
 	 */
 	if (tick_do_timer_cpu == dying_cpu)
 		tick_do_timer_cpu = cpumask_first(cpu_online_mask);

kernel/time/tick-sched.c

@@ -8,6 +8,7 @@
  *
  *  Started by: Thomas Gleixner and Ingo Molnar
  */
+#include <linux/compiler.h>
 #include <linux/cpu.h>
 #include <linux/err.h>
 #include <linux/hrtimer.h>
@@ -204,7 +205,7 @@ static inline void tick_sched_flag_clear(struct tick_sched *ts,
 
 static void tick_sched_do_timer(struct tick_sched *ts, ktime_t now)
 {
-	int cpu = smp_processor_id();
+	int tick_cpu, cpu = smp_processor_id();
 
 	/*
 	 * Check if the do_timer duty was dropped. We don't care about
@@ -216,16 +217,18 @@ static void tick_sched_do_timer(struct tick_sched *ts, ktime_t now)
 	 * If nohz_full is enabled, this should not happen because the
 	 * 'tick_do_timer_cpu' CPU never relinquishes.
 	 */
-	if (IS_ENABLED(CONFIG_NO_HZ_COMMON) &&
+	tick_cpu = READ_ONCE(tick_do_timer_cpu);
-	    unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE)) {
+
+	if (IS_ENABLED(CONFIG_NO_HZ_COMMON) && unlikely(tick_cpu == TICK_DO_TIMER_NONE)) {
 #ifdef CONFIG_NO_HZ_FULL
 		WARN_ON_ONCE(tick_nohz_full_running);
 #endif
-		tick_do_timer_cpu = cpu;
+		WRITE_ONCE(tick_do_timer_cpu, cpu);
+		tick_cpu = cpu;
 	}
 
 	/* Check if jiffies need an update */
-	if (tick_do_timer_cpu == cpu)
+	if (tick_cpu == cpu)
 		tick_do_update_jiffies64(now);
 
 	/*
@@ -610,7 +613,7 @@ bool tick_nohz_cpu_hotpluggable(unsigned int cpu)
 	 * timers, workqueues, timekeeping, ...) on behalf of full dynticks
 	 * CPUs. It must remain online when nohz full is enabled.
 	 */
-	if (tick_nohz_full_running && tick_do_timer_cpu == cpu)
+	if (tick_nohz_full_running && READ_ONCE(tick_do_timer_cpu) == cpu)
 		return false;
 	return true;
 }
@@ -891,6 +894,7 @@ static ktime_t tick_nohz_next_event(struct tick_sched *ts, int cpu)
 {
 	u64 basemono, next_tick, delta, expires;
 	unsigned long basejiff;
+	int tick_cpu;
 
 	basemono = get_jiffies_update(&basejiff);
 	ts->last_jiffies = basejiff;
@@ -947,9 +951,9 @@ static ktime_t tick_nohz_next_event(struct tick_sched *ts, int cpu)
 	 * Otherwise we can sleep as long as we want.
 	 */
 	delta = timekeeping_max_deferment();
-	if (cpu != tick_do_timer_cpu &&
+	tick_cpu = READ_ONCE(tick_do_timer_cpu);
-	    (tick_do_timer_cpu != TICK_DO_TIMER_NONE ||
+	if (tick_cpu != cpu &&
-	     !tick_sched_flag_test(ts, TS_FLAG_DO_TIMER_LAST)))
+	    (tick_cpu != TICK_DO_TIMER_NONE || !tick_sched_flag_test(ts, TS_FLAG_DO_TIMER_LAST)))
 		delta = KTIME_MAX;
 
 	/* Calculate the next expiry time */
@@ -970,6 +974,7 @@ static void tick_nohz_stop_tick(struct tick_sched *ts, int cpu)
 	unsigned long basejiff = ts->last_jiffies;
 	u64 basemono = ts->timer_expires_base;
 	bool timer_idle = tick_sched_flag_test(ts, TS_FLAG_STOPPED);
+	int tick_cpu;
 	u64 expires;
 
 	/* Make sure we won't be trying to stop it twice in a row. */
@@ -1007,10 +1012,11 @@ static void tick_nohz_stop_tick(struct tick_sched *ts, int cpu)
 	 * do_timer() never gets invoked. Keep track of the fact that it
 	 * was the one which had the do_timer() duty last.
 	 */
-	if (cpu == tick_do_timer_cpu) {
+	tick_cpu = READ_ONCE(tick_do_timer_cpu);
-		tick_do_timer_cpu = TICK_DO_TIMER_NONE;
+	if (tick_cpu == cpu) {
+		WRITE_ONCE(tick_do_timer_cpu, TICK_DO_TIMER_NONE);
 		tick_sched_flag_set(ts, TS_FLAG_DO_TIMER_LAST);
-	} else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) {
+	} else if (tick_cpu != TICK_DO_TIMER_NONE) {
 		tick_sched_flag_clear(ts, TS_FLAG_DO_TIMER_LAST);
 	}
 
@@ -1173,15 +1179,17 @@ static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
 		return false;
 
 	if (tick_nohz_full_enabled()) {
+		int tick_cpu = READ_ONCE(tick_do_timer_cpu);
+
 		/*
 		 * Keep the tick alive to guarantee timekeeping progression
 		 * if there are full dynticks CPUs around
 		 */
-		if (tick_do_timer_cpu == cpu)
+		if (tick_cpu == cpu)
 			return false;
 
 		/* Should not happen for nohz-full */
-		if (WARN_ON_ONCE(tick_do_timer_cpu == TICK_DO_TIMER_NONE))
+		if (WARN_ON_ONCE(tick_cpu == TICK_DO_TIMER_NONE))
 			return false;
 	}
 

tools/testing/selftests/kselftest.h

@@ -51,6 +51,7 @@
 #include <stdarg.h>
 #include <string.h>
 #include <stdio.h>
+#include <sys/utsname.h>
 #endif
 
 #ifndef ARRAY_SIZE
@@ -79,6 +80,9 @@
 #define KSFT_XPASS 3
 #define KSFT_SKIP  4
 
+#ifndef __noreturn
+#define __noreturn       __attribute__((__noreturn__))
+#endif
 #define __printf(a, b)   __attribute__((format(printf, a, b)))
 
 /* counters */
@@ -299,13 +303,13 @@ void ksft_test_result_code(int exit_code, const char *test_name,
 	va_end(args);
 }
 
-static inline int ksft_exit_pass(void)
+static inline __noreturn int ksft_exit_pass(void)
 {
 	ksft_print_cnts();
 	exit(KSFT_PASS);
 }
 
-static inline int ksft_exit_fail(void)
+static inline __noreturn int ksft_exit_fail(void)
 {
 	ksft_print_cnts();
 	exit(KSFT_FAIL);
@@ -332,7 +336,7 @@ static inline int ksft_exit_fail(void)
 		  ksft_cnt.ksft_xfail +	\
 		  ksft_cnt.ksft_xskip)
 
-static inline __printf(1, 2) int ksft_exit_fail_msg(const char *msg, ...)
+static inline __noreturn __printf(1, 2) int ksft_exit_fail_msg(const char *msg, ...)
 {
 	int saved_errno = errno;
 	va_list args;
@@ -347,19 +351,19 @@ static inline __printf(1, 2) int ksft_exit_fail_msg(const char *msg, ...)
 	exit(KSFT_FAIL);
 }
 
-static inline int ksft_exit_xfail(void)
+static inline __noreturn int ksft_exit_xfail(void)
 {
 	ksft_print_cnts();
 	exit(KSFT_XFAIL);
 }
 
-static inline int ksft_exit_xpass(void)
+static inline __noreturn int ksft_exit_xpass(void)
 {
 	ksft_print_cnts();
 	exit(KSFT_XPASS);
 }
 
-static inline __printf(1, 2) int ksft_exit_skip(const char *msg, ...)
+static inline __noreturn __printf(1, 2) int ksft_exit_skip(const char *msg, ...)
 {
 	int saved_errno = errno;
 	va_list args;
@@ -388,4 +392,21 @@ static inline __printf(1, 2) int ksft_exit_skip(const char *msg, ...)
 	exit(KSFT_SKIP);
 }
 
+static inline int ksft_min_kernel_version(unsigned int min_major,
+					  unsigned int min_minor)
+{
+#ifdef NOLIBC
+	ksft_print_msg("NOLIBC: Can't check kernel version: Function not implemented\n");
+	return 0;
+#else
+	unsigned int major, minor;
+	struct utsname info;
+
+	if (uname(&info) || sscanf(info.release, "%u.%u.", &major, &minor) != 2)
+		ksft_exit_fail_msg("Can't parse kernel version\n");
+
+	return major > min_major || (major == min_major && minor >= min_minor);
+#endif
+}
+
 #endif /* __KSELFTEST_H */

tools/testing/selftests/timers/posix_timers.c

@@ -66,7 +66,7 @@ static int check_diff(struct timeval start, struct timeval end)
 	diff = end.tv_usec - start.tv_usec;
 	diff += (end.tv_sec - start.tv_sec) * USECS_PER_SEC;
 
-	if (abs(diff - DELAY * USECS_PER_SEC) > USECS_PER_SEC / 2) {
+	if (llabs(diff - DELAY * USECS_PER_SEC) > USECS_PER_SEC / 2) {
 		printf("Diff too high: %lld..", diff);
 		return -1;
 	}
@@ -184,80 +184,71 @@ static int check_timer_create(int which)
 	return 0;
 }
 
-int remain;
+static pthread_t ctd_thread;
-__thread int got_signal;
+static volatile int ctd_count, ctd_failed;
 
-static void *distribution_thread(void *arg)
+static void ctd_sighandler(int sig)
 {
-	while (__atomic_load_n(&remain, __ATOMIC_RELAXED));
+	if (pthread_self() != ctd_thread)
-	return NULL;
+		ctd_failed = 1;
+	ctd_count--;
 }
 
-static void distribution_handler(int nr)
+static void *ctd_thread_func(void *arg)
 {
-	if (!__atomic_exchange_n(&got_signal, 1, __ATOMIC_RELAXED))
-		__atomic_fetch_sub(&remain, 1, __ATOMIC_RELAXED);
-}
-
-/*
- * Test that all running threads _eventually_ receive CLOCK_PROCESS_CPUTIME_ID
- * timer signals. This primarily tests that the kernel does not favour any one.
- */
-static int check_timer_distribution(void)
-{
-	int err, i;
-	timer_t id;
-	const int nthreads = 10;
-	pthread_t threads[nthreads];
 	struct itimerspec val = {
 		.it_value.tv_sec = 0,
 		.it_value.tv_nsec = 1000 * 1000,
 		.it_interval.tv_sec = 0,
 		.it_interval.tv_nsec = 1000 * 1000,
 	};
+	timer_t id;
 
-	remain = nthreads + 1;  /* worker threads + this thread */
+	/* 1/10 seconds to ensure the leader sleeps */
-	signal(SIGALRM, distribution_handler);
+	usleep(10000);
-	err = timer_create(CLOCK_PROCESS_CPUTIME_ID, NULL, &id);
-	if (err < 0) {
-		ksft_perror("Can't create timer");
-		return -1;
-	}
-	err = timer_settime(id, 0, &val, NULL);
-	if (err < 0) {
-		ksft_perror("Can't set timer");
-		return -1;
-	}
 
-	for (i = 0; i < nthreads; i++) {
+	ctd_count = 100;
-		err = pthread_create(&threads[i], NULL, distribution_thread,
+	if (timer_create(CLOCK_PROCESS_CPUTIME_ID, NULL, &id))
-				     NULL);
+		return "Can't create timer\n";
-		if (err) {
+	if (timer_settime(id, 0, &val, NULL))
-			ksft_print_msg("Can't create thread: %s (%d)\n",
+		return "Can't set timer\n";
-				       strerror(errno), errno);
-			return -1;
-		}
-	}
 
-	/* Wait for all threads to receive the signal. */
+	while (ctd_count > 0 && !ctd_failed)
-	while (__atomic_load_n(&remain, __ATOMIC_RELAXED));
+		;
 
-	for (i = 0; i < nthreads; i++) {
+	if (timer_delete(id))
-		err = pthread_join(threads[i], NULL);
+		return "Can't delete timer\n";
-		if (err) {
-			ksft_print_msg("Can't join thread: %s (%d)\n",
-				       strerror(errno), errno);
-			return -1;
-		}
-	}
 
-	if (timer_delete(id)) {
+	return NULL;
-		ksft_perror("Can't delete timer");
+}
-		return -1;
-	}
 
-	ksft_test_result_pass("check_timer_distribution\n");
+/*
+ * Test that only the running thread receives the timer signal.
+ */
+static int check_timer_distribution(void)
+{
+	const char *errmsg;
+
+	signal(SIGALRM, ctd_sighandler);
+
+	errmsg = "Can't create thread\n";
+	if (pthread_create(&ctd_thread, NULL, ctd_thread_func, NULL))
+		goto err;
+
+	errmsg = "Can't join thread\n";
+	if (pthread_join(ctd_thread, (void **)&errmsg) || errmsg)
+		goto err;
+
+	if (!ctd_failed)
+		ksft_test_result_pass("check signal distribution\n");
+	else if (ksft_min_kernel_version(6, 3))
+		ksft_test_result_fail("check signal distribution\n");
+	else
+		ksft_test_result_skip("check signal distribution (old kernel)\n");
 	return 0;
+err:
+	ksft_print_msg("%s", errmsg);
+	return -1;
 }
 
 int main(int argc, char **argv)

tools/testing/selftests/timers/valid-adjtimex.c

@@ -21,9 +21,6 @@
  *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  *   GNU General Public License for more details.
  */
-
-
-
 #include <stdio.h>
 #include <stdlib.h>
 #include <time.h>
@@ -62,45 +59,47 @@ int clear_time_state(void)
 #define NUM_FREQ_OUTOFRANGE 4
 #define NUM_FREQ_INVALID 2
 
+#define SHIFTED_PPM (1 << 16)
+
 long valid_freq[NUM_FREQ_VALID] = {
-	-499<<16,
+	 -499 * SHIFTED_PPM,
-	-450<<16,
+	 -450 * SHIFTED_PPM,
-	-400<<16,
+	 -400 * SHIFTED_PPM,
-	-350<<16,
+	 -350 * SHIFTED_PPM,
-	-300<<16,
+	 -300 * SHIFTED_PPM,
-	-250<<16,
+	 -250 * SHIFTED_PPM,
-	-200<<16,
+	 -200 * SHIFTED_PPM,
-	-150<<16,
+	 -150 * SHIFTED_PPM,
-	-100<<16,
+	 -100 * SHIFTED_PPM,
-	-75<<16,
+	  -75 * SHIFTED_PPM,
-	-50<<16,
+	  -50 * SHIFTED_PPM,
-	-25<<16,
+	  -25 * SHIFTED_PPM,
-	-10<<16,
+	  -10 * SHIFTED_PPM,
-	-5<<16,
+	   -5 * SHIFTED_PPM,
-	-1<<16,
+	   -1 * SHIFTED_PPM,
 	-1000,
-	1<<16,
+	    1 * SHIFTED_PPM,
-	5<<16,
+	    5 * SHIFTED_PPM,
-	10<<16,
+	   10 * SHIFTED_PPM,
-	25<<16,
+	   25 * SHIFTED_PPM,
-	50<<16,
+	   50 * SHIFTED_PPM,
-	75<<16,
+	   75 * SHIFTED_PPM,
-	100<<16,
+	  100 * SHIFTED_PPM,
-	150<<16,
+	  150 * SHIFTED_PPM,
-	200<<16,
+	  200 * SHIFTED_PPM,
-	250<<16,
+	  250 * SHIFTED_PPM,
-	300<<16,
+	  300 * SHIFTED_PPM,
-	350<<16,
+	  350 * SHIFTED_PPM,
-	400<<16,
+	  400 * SHIFTED_PPM,
-	450<<16,
+	  450 * SHIFTED_PPM,
-	499<<16,
+	  499 * SHIFTED_PPM,
 };
 
 long outofrange_freq[NUM_FREQ_OUTOFRANGE] = {
-	-1000<<16,
+	-1000 * SHIFTED_PPM,
-	-550<<16,
+	 -550 * SHIFTED_PPM,
-	550<<16,
+	  550 * SHIFTED_PPM,
-	1000<<16,
+	 1000 * SHIFTED_PPM,
 };
 
 #define LONG_MAX (~0UL>>1)