hrtimer: Reverse patch to switch sys_nanosleep to hrtimer

Patch 6ba1b912 hrtimer: switch
sys_nanosleep to hrtimer breaks dynamic tick. All usleep calls
will fail as the next_timer_interrupt currently does not scan
hrtimer queues. This means the system will be potentially
asleep in the idle mode when the next hrtimer is supposed to
run. Until hrtimer_next_interrupt is implemented, we'll use
the old sys_nanosleep.

kernel/hrtimer.c

@@ -727,20 +727,6 @@ long hrtimer_nanosleep(struct timespec *rqtp, struct timespec __user *rmtp,
 	return -ERESTART_RESTARTBLOCK;
 }
 
-asmlinkage long
-sys_nanosleep(struct timespec __user *rqtp, struct timespec __user *rmtp)
-{
-	struct timespec tu;
-
-	if (copy_from_user(&tu, rqtp, sizeof(tu)))
-		return -EFAULT;
-
-	if (!timespec_valid(&tu))
-		return -EINVAL;
-
-	return hrtimer_nanosleep(&tu, rmtp, HRTIMER_REL, CLOCK_MONOTONIC);
-}
-
 /*
  * Functions related to boot-time initialization:
  */

kernel/timer.c

@@ -1149,6 +1149,62 @@ asmlinkage long sys_gettid(void)
 	return current->pid;
 }
 
+static long __sched nanosleep_restart(struct restart_block *restart)
+{
+	unsigned long expire = restart->arg0, now = jiffies;
+	struct timespec __user *rmtp = (struct timespec __user *) restart->arg1;
+	long ret;
+
+	/* Did it expire while we handled signals? */
+	if (!time_after(expire, now))
+		return 0;
+
+	expire = schedule_timeout_interruptible(expire - now);
+
+	ret = 0;
+	if (expire) {
+		struct timespec t;
+		jiffies_to_timespec(expire, &t);
+
+		ret = -ERESTART_RESTARTBLOCK;
+		if (rmtp && copy_to_user(rmtp, &t, sizeof(t)))
+			ret = -EFAULT;
+		/* The 'restart' block is already filled in */
+	}
+	return ret;
+}
+
+asmlinkage long sys_nanosleep(struct timespec __user *rqtp, struct timespec __user *rmtp)
+{
+	struct timespec t;
+	unsigned long expire;
+	long ret;
+
+	if (copy_from_user(&t, rqtp, sizeof(t)))
+		return -EFAULT;
+
+	if ((t.tv_nsec >= 1000000000L) || (t.tv_nsec < 0) || (t.tv_sec < 0))
+		return -EINVAL;
+
+	expire = timespec_to_jiffies(&t) + (t.tv_sec || t.tv_nsec);
+	expire = schedule_timeout_interruptible(expire);
+
+	ret = 0;
+	if (expire) {
+		struct restart_block *restart;
+		jiffies_to_timespec(expire, &t);
+		if (rmtp && copy_to_user(rmtp, &t, sizeof(t)))
+			return -EFAULT;
+
+		restart = &current_thread_info()->restart_block;
+		restart->fn = nanosleep_restart;
+		restart->arg0 = jiffies + expire;
+		restart->arg1 = (unsigned long) rmtp;
+		ret = -ERESTART_RESTARTBLOCK;
+	}
+	return ret;
+}
+
 /*
  * sys_sysinfo - fill in sysinfo struct
  */