signals: Use hrtimer for sigtimedwait()

We've converted most timeout related syscalls to hrtimers, but
sigtimedwait() did not get this treatment.

Convert it so we get a reasonable accuracy and remove the
user space exposure to the timer wheel properties.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Arjan van de Ven <arjan@infradead.org>
Cc: Chris Mason <clm@fb.com>
Cc: Cyril Hrubis <chrubis@suse.cz>
Cc: George Spelvin <linux@sciencehorizons.net>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Len Brown <lenb@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: rt@linutronix.de
Link: http://lkml.kernel.org/r/20160704094341.787164909@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/signal.c

@@ -2751,23 +2751,18 @@ int copy_siginfo_to_user(siginfo_t __user *to, const siginfo_t *from)
  *  @ts: upper bound on process time suspension
  */
 int do_sigtimedwait(const sigset_t *which, siginfo_t *info,
-			const struct timespec *ts)
+		    const struct timespec *ts)
 {
+	ktime_t *to = NULL, timeout = { .tv64 = KTIME_MAX };
 	struct task_struct *tsk = current;
-	long timeout = MAX_SCHEDULE_TIMEOUT;
 	sigset_t mask = *which;
-	int sig;
+	int sig, ret = 0;
 
 	if (ts) {
 		if (!timespec_valid(ts))
 			return -EINVAL;
-		timeout = timespec_to_jiffies(ts);
-		/*
-		 * We can be close to the next tick, add another one
-		 * to ensure we will wait at least the time asked for.
-		 */
-		if (ts->tv_sec || ts->tv_nsec)
-			timeout++;
+		timeout = timespec_to_ktime(*ts);
+		to = &timeout;
 	}
 
 	/*
@@ -2778,7 +2773,7 @@ int do_sigtimedwait(const sigset_t *which, siginfo_t *info,
 
 	spin_lock_irq(&tsk->sighand->siglock);
 	sig = dequeue_signal(tsk, &mask, info);
-	if (!sig && timeout) {
+	if (!sig && timeout.tv64) {
 		/*
 		 * None ready, temporarily unblock those we're interested
 		 * while we are sleeping in so that we'll be awakened when
@@ -2790,8 +2785,9 @@ int do_sigtimedwait(const sigset_t *which, siginfo_t *info,
 		recalc_sigpending();
 		spin_unlock_irq(&tsk->sighand->siglock);
 
-		timeout = freezable_schedule_timeout_interruptible(timeout);
-
+		__set_current_state(TASK_INTERRUPTIBLE);
+		ret = freezable_schedule_hrtimeout_range(to, tsk->timer_slack_ns,
+							 HRTIMER_MODE_REL);
 		spin_lock_irq(&tsk->sighand->siglock);
 		__set_task_blocked(tsk, &tsk->real_blocked);
 		sigemptyset(&tsk->real_blocked);
@@ -2801,7 +2797,7 @@ int do_sigtimedwait(const sigset_t *which, siginfo_t *info,
 
 	if (sig)
 		return sig;
-	return timeout ? -EINTR : -EAGAIN;
+	return ret ? -EINTR : -EAGAIN;
 }
 
 /**