Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull scheduler fixes from Ingo Molnar:
 "Misc fixes"

* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/deadline: Fix deadline parameter modification handling
  sched/wait: Remove might_sleep() from wait_event_cmd()
  sched: Fix crash if cpuset_cpumask_can_shrink() is passed an empty cpumask
  sched/fair: Avoid using uninitialized variable in preferred_group_nid()

4 files changed, 34 insertions, 8 deletions

diff --git a/include/linux/wait.h b/include/linux/wait.h
index 2232ed16635a..37423e0e1379 100644
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -363,7 +363,6 @@ do {									\
  */
 #define wait_event_cmd(wq, condition, cmd1, cmd2)                       \
 do {                                                                    \
-        might_sleep();                                                  \
         if (condition)                                                  \
                 break;                                                  \
         __wait_event_cmd(wq, condition, cmd1, cmd2);                    \
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e628cb11b560..5eab11d4b747 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1814,6 +1814,10 @@ void __dl_clear_params(struct task_struct *p)
         dl_se->dl_period = 0;
         dl_se->flags = 0;
         dl_se->dl_bw = 0;
+
+        dl_se->dl_throttled = 0;
+        dl_se->dl_new = 1;
+        dl_se->dl_yielded = 0;
 }
 
 /*
@@ -1839,7 +1843,7 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
 #endif
 
         RB_CLEAR_NODE(&p->dl.rb_node);
-        hrtimer_init(&p->dl.dl_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+        init_dl_task_timer(&p->dl);
         __dl_clear_params(p);
 
         INIT_LIST_HEAD(&p->rt.run_list);
@@ -2049,6 +2053,9 @@ static inline int dl_bw_cpus(int i)
  * allocated bandwidth to reflect the new situation.
  *
  * This function is called while holding p's rq->lock.
+ *
+ * XXX we should delay bw change until the task's 0-lag point, see
+ * __setparam_dl().
  */
 static int dl_overflow(struct task_struct *p, int policy,
                        const struct sched_attr *attr)
@@ -3251,15 +3258,31 @@ __setparam_dl(struct task_struct *p, const struct sched_attr *attr)
 {
         struct sched_dl_entity *dl_se = &p->dl;
 
-        init_dl_task_timer(dl_se);
         dl_se->dl_runtime = attr->sched_runtime;
         dl_se->dl_deadline = attr->sched_deadline;
         dl_se->dl_period = attr->sched_period ?: dl_se->dl_deadline;
         dl_se->flags = attr->sched_flags;
         dl_se->dl_bw = to_ratio(dl_se->dl_period, dl_se->dl_runtime);
-        dl_se->dl_throttled = 0;
-        dl_se->dl_new = 1;
-        dl_se->dl_yielded = 0;
+
+        /*
+         * Changing the parameters of a task is 'tricky' and we're not doing
+         * the correct thing -- also see task_dead_dl() and switched_from_dl().
+         *
+         * What we SHOULD do is delay the bandwidth release until the 0-lag
+         * point. This would include retaining the task_struct until that time
+         * and change dl_overflow() to not immediately decrement the current
+         * amount.
+         *
+         * Instead we retain the current runtime/deadline and let the new
+         * parameters take effect after the current reservation period lapses.
+         * This is safe (albeit pessimistic) because the 0-lag point is always
+         * before the current scheduling deadline.
+         *
+         * We can still have temporary overloads because we do not delay the
+         * change in bandwidth until that time; so admission control is
+         * not on the safe side. It does however guarantee tasks will never
+         * consume more than promised.
+         */
 }
 
 /*
@@ -4642,6 +4665,9 @@ int cpuset_cpumask_can_shrink(const struct cpumask *cur,
         struct dl_bw *cur_dl_b;
         unsigned long flags;
 
+        if (!cpumask_weight(cur))
+                return ret;
+
         rcu_read_lock_sched();
         cur_dl_b = dl_bw_of(cpumask_any(cur));
         trial_cpus = cpumask_weight(trial);
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index b52092f2636d..726470d47f87 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1094,6 +1094,7 @@ static void task_dead_dl(struct task_struct *p)
          * Since we are TASK_DEAD we won't slip out of the domain!
          */
         raw_spin_lock_irq(&dl_b->lock);
+        /* XXX we should retain the bw until 0-lag */
         dl_b->total_bw -= p->dl.dl_bw;
         raw_spin_unlock_irq(&dl_b->lock);
 
@@ -1614,8 +1615,8 @@ static void cancel_dl_timer(struct rq *rq, struct task_struct *p)
 
 static void switched_from_dl(struct rq *rq, struct task_struct *p)
 {
+        /* XXX we should retain the bw until 0-lag */
         cancel_dl_timer(rq, p);
-
         __dl_clear_params(p);
 
         /*
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 40667cbf371b..fe331fc391f5 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1730,7 +1730,7 @@ static int preferred_group_nid(struct task_struct *p, int nid)
         nodes = node_online_map;
         for (dist = sched_max_numa_distance; dist > LOCAL_DISTANCE; dist--) {
                 unsigned long max_faults = 0;
-                nodemask_t max_group;
+                nodemask_t max_group = NODE_MASK_NONE;
                 int a, b;
 
                 /* Are there nodes at this distance from each other? */