sched: rt-watchdog: fix .rlim_max = RLIM_INFINITY

Remove the curious logic to set it_sched_expires in the future. It useless
because rt.timeout wouldn't be incremented anyway.

Explicity check for RLIM_INFINITY as a test programm that had a 1s soft limit
and a inf hard limit would SIGKILL at 1s. This is because RLIM_INFINITY+d-1
is d-2.

Signed-off-by: Peter Zijlsta <a.p.zijlstra@chello.nl>
CC: Michal Schmidt <mschmidt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/posix-cpu-timers.c

@@ -1020,7 +1020,8 @@ static void check_thread_timers(struct task_struct *tsk,
 		unsigned long hard = sig->rlim[RLIMIT_RTTIME].rlim_max;
 		unsigned long *soft = &sig->rlim[RLIMIT_RTTIME].rlim_cur;
 
-		if (tsk->rt.timeout > DIV_ROUND_UP(hard, USEC_PER_SEC/HZ)) {
+		if (hard != RLIM_INFINITY &&
+		    tsk->rt.timeout > DIV_ROUND_UP(hard, USEC_PER_SEC/HZ)) {
 			/*
 			 * At the hard limit, we just die.
 			 * No need to calculate anything else now.

kernel/sched_rt.c

@@ -1125,13 +1125,7 @@ static void watchdog(struct rq *rq, struct task_struct *p)
 
 		p->rt.timeout++;
 		next = DIV_ROUND_UP(min(soft, hard), USEC_PER_SEC/HZ);
-		if (next > p->rt.timeout) {
-			u64 next_time = p->se.sum_exec_runtime;
-
-			next_time += next * (NSEC_PER_SEC/HZ);
-			if (p->it_sched_expires > next_time)
-				p->it_sched_expires = next_time;
-		} else
+		if (p->rt.timeout > next)
 			p->it_sched_expires = p->se.sum_exec_runtime;
 	}
 }