posix-cpu-timers: Move copyout of timespec into do_cpu_nanosleep()

The posix-cpu-timer nanosleep() implementation can be simplified by moving
the copy out of the remaining time to do_cpu_nanosleep() which is shared
between the real nanosleep function and the restart function.

The pointer to the timespec64 which is updated has to be stored in the
restart block anyway. Instead of storing it only in the restart case, store
it before calling do_cpu_nanosleep() and copy the remaining time in the
signal exit path.

[ tglx: Added changelog ]
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20170607084241.28657-1-viro@ZenIV.linux.org.uk

kernel/time/posix-cpu-timers.c

@@ -1226,9 +1226,10 @@ void set_process_cpu_timer(struct task_struct *tsk, unsigned int clock_idx,
 }
 
 static int do_cpu_nanosleep(const clockid_t which_clock, int flags,
-			    struct timespec64 *rqtp, struct itimerspec64 *it)
+			    struct timespec64 *rqtp)
 {
 	struct k_itimer timer;
+	struct itimerspec64 it;
 	int error;
 
 	/*
@@ -1242,12 +1243,14 @@ static int do_cpu_nanosleep(const clockid_t which_clock, int flags,
 	timer.it_process = current;
 	if (!error) {
 		static struct itimerspec64 zero_it;
+		struct restart_block *restart = &current->restart_block;
+		struct timespec __user *rmtp;
 
-		memset(it, 0, sizeof *it);
-		it->it_value = *rqtp;
+		memset(&it, 0, sizeof it);
+		it.it_value = *rqtp;
 
 		spin_lock_irq(&timer.it_lock);
-		error = posix_cpu_timer_set(&timer, flags, it, NULL);
+		error = posix_cpu_timer_set(&timer, flags, &it, NULL);
 		if (error) {
 			spin_unlock_irq(&timer.it_lock);
 			return error;
@@ -1277,7 +1280,7 @@ static int do_cpu_nanosleep(const clockid_t which_clock, int flags,
 		 * We were interrupted by a signal.
 		 */
 		*rqtp = ns_to_timespec64(timer.it.cpu.expires);
-		error = posix_cpu_timer_set(&timer, 0, &zero_it, it);
+		error = posix_cpu_timer_set(&timer, 0, &zero_it, &it);
 		if (!error) {
 			/*
 			 * Timer is now unarmed, deletion can not fail.
@@ -1297,7 +1300,7 @@ static int do_cpu_nanosleep(const clockid_t which_clock, int flags,
 			spin_unlock_irq(&timer.it_lock);
 		}
 
-		if ((it->it_value.tv_sec | it->it_value.tv_nsec) == 0) {
+		if ((it.it_value.tv_sec | it.it_value.tv_nsec) == 0) {
 			/*
 			 * It actually did fire already.
 			 */
@@ -1305,6 +1308,18 @@ static int do_cpu_nanosleep(const clockid_t which_clock, int flags,
 		}
 
 		error = -ERESTART_RESTARTBLOCK;
+		/*
+		 * Report back to the user the time still remaining.
+		 */
+		rmtp = restart->nanosleep.rmtp;
+		if (rmtp) {
+			struct timespec ts;
+
+			ts = timespec64_to_timespec(it.it_value);
+			if (copy_to_user(rmtp, &ts, sizeof(*rmtp)))
+				return -EFAULT;
+		}
+		restart->nanosleep.expires = timespec64_to_ns(rqtp);
 	}
 
 	return error;
@@ -1316,10 +1331,13 @@ static int posix_cpu_nsleep(const clockid_t which_clock, int flags,
 			    struct timespec64 *rqtp, struct timespec __user *rmtp)
 {
 	struct restart_block *restart_block = &current->restart_block;
-	struct itimerspec64 it;
-	struct timespec ts;
 	int error;
 
+	if (flags & TIMER_ABSTIME)
+		rmtp = NULL;
+
+	restart_block->nanosleep.rmtp = rmtp;
+
 	/*
 	 * Diagnose required errors first.
 	 */
@@ -1328,23 +1346,15 @@ static int posix_cpu_nsleep(const clockid_t which_clock, int flags,
 	     CPUCLOCK_PID(which_clock) == task_pid_vnr(current)))
 		return -EINVAL;
 
-	error = do_cpu_nanosleep(which_clock, flags, rqtp, &it);
+	error = do_cpu_nanosleep(which_clock, flags, rqtp);
 
 	if (error == -ERESTART_RESTARTBLOCK) {
 
 		if (flags & TIMER_ABSTIME)
 			return -ERESTARTNOHAND;
-		/*
-		 * Report back to the user the time still remaining.
-		 */
-		ts = timespec64_to_timespec(it.it_value);
-		if (rmtp && copy_to_user(rmtp, &ts, sizeof(*rmtp)))
-			return -EFAULT;
 
 		restart_block->fn = posix_cpu_nsleep_restart;
 		restart_block->nanosleep.clockid = which_clock;
-		restart_block->nanosleep.rmtp = rmtp;
-		restart_block->nanosleep.expires = timespec64_to_ns(rqtp);
 	}
 	return error;
 }
@@ -1352,28 +1362,11 @@ static int posix_cpu_nsleep(const clockid_t which_clock, int flags,
 static long posix_cpu_nsleep_restart(struct restart_block *restart_block)
 {
 	clockid_t which_clock = restart_block->nanosleep.clockid;
-	struct itimerspec64 it;
 	struct timespec64 t;
-	struct timespec tmp;
-	int error;
 
 	t = ns_to_timespec64(restart_block->nanosleep.expires);
 
-	error = do_cpu_nanosleep(which_clock, TIMER_ABSTIME, &t, &it);
-
-	if (error == -ERESTART_RESTARTBLOCK) {
-		struct timespec __user *rmtp = restart_block->nanosleep.rmtp;
-		/*
-		 * Report back to the user the time still remaining.
-		 */
-		 tmp = timespec64_to_timespec(it.it_value);
-		if (rmtp && copy_to_user(rmtp, &tmp, sizeof(*rmtp)))
-			return -EFAULT;
-
-		restart_block->nanosleep.expires = timespec64_to_ns(&t);
-	}
-	return error;
-
+	return do_cpu_nanosleep(which_clock, TIMER_ABSTIME, &t);
 }
 
 #define PROCESS_CLOCK	MAKE_PROCESS_CPUCLOCK(0, CPUCLOCK_SCHED)