1 files changed, 21 insertions, 6 deletions

diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index 479b16b44f79..7c3e1e6dfb5b 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -88,6 +88,19 @@ static inline union cpu_time_count cpu_time_sub(const clockid_t which_clock,
 }
 
 /*
+ * 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;
                 }