---

yaml
---
r: 39715
b: refs/heads/master
c: ac08c26
h: refs/heads/master
i:
  39713: b6f25cd
  39711: ae1990a
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: e24650c2e744f99541125a5b023f0d02cad19d14
+refs/heads/master: ac08c26492a0ad4d94a25bd47d5630cd38337069

trunk/kernel/posix-cpu-timers.c

@@ -87,6 +87,19 @@ static inline union cpu_time_count cpu_time_sub(const clockid_t which_clock,
 	return a;
 }
 
+/*
+ * Divide and limit the result to res >= 1
+ *
+ * This is necessary to prevent signal delivery starvation, when the result of
+ * the division would be rounded down to 0.
+ */
+static inline cputime_t cputime_div_non_zero(cputime_t time, unsigned long div)
+{
+	cputime_t res = cputime_div(time, div);
+
+	return max_t(cputime_t, res, 1);
+}
+
 /*
  * Update expiry time from increment, and increase overrun count,
  * given the current clock sample.
@@ -483,8 +496,8 @@ static void process_timer_rebalance(struct task_struct *p,
 		BUG();
 		break;
 	case CPUCLOCK_PROF:
-		left = cputime_div(cputime_sub(expires.cpu, val.cpu),
-				   nthreads);
+		left = cputime_div_non_zero(cputime_sub(expires.cpu, val.cpu),
+				       nthreads);
 		do {
 			if (likely(!(t->flags & PF_EXITING))) {
 				ticks = cputime_add(prof_ticks(t), left);
@@ -498,8 +511,8 @@ static void process_timer_rebalance(struct task_struct *p,
 		} while (t != p);
 		break;
 	case CPUCLOCK_VIRT:
-		left = cputime_div(cputime_sub(expires.cpu, val.cpu),
-				   nthreads);
+		left = cputime_div_non_zero(cputime_sub(expires.cpu, val.cpu),
+				       nthreads);
 		do {
 			if (likely(!(t->flags & PF_EXITING))) {
 				ticks = cputime_add(virt_ticks(t), left);
@@ -515,6 +528,7 @@ static void process_timer_rebalance(struct task_struct *p,
 	case CPUCLOCK_SCHED:
 		nsleft = expires.sched - val.sched;
 		do_div(nsleft, nthreads);
+		nsleft = max_t(unsigned long long, nsleft, 1);
 		do {
 			if (likely(!(t->flags & PF_EXITING))) {
 				ns = t->sched_time + nsleft;
@@ -1159,12 +1173,13 @@ static void check_process_timers(struct task_struct *tsk,
 
 		prof_left = cputime_sub(prof_expires, utime);
 		prof_left = cputime_sub(prof_left, stime);
-		prof_left = cputime_div(prof_left, nthreads);
+		prof_left = cputime_div_non_zero(prof_left, nthreads);
 		virt_left = cputime_sub(virt_expires, utime);
-		virt_left = cputime_div(virt_left, nthreads);
+		virt_left = cputime_div_non_zero(virt_left, nthreads);
 		if (sched_expires) {
 			sched_left = sched_expires - sched_time;
 			do_div(sched_left, nthreads);
+			sched_left = max_t(unsigned long long, sched_left, 1);
 		} else {
 			sched_left = 0;
 		}