1 files changed, 63 insertions, 26 deletions

diff --git a/kernel/sched_cpupri.c b/kernel/sched_cpupri.c
index 2722dc1b4138..a86cf9d9eb11 100644
--- a/kernel/sched_cpupri.c
+++ b/kernel/sched_cpupri.c
@@ -47,9 +47,6 @@ static int convert_prio(int prio)
         return cpupri;
 }
 
-#define for_each_cpupri_active(array, idx)                    \
-        for_each_set_bit(idx, array, CPUPRI_NR_PRIORITIES)
-
 /**
  * cpupri_find - find the best (lowest-pri) CPU in the system
  * @cp: The cpupri context
@@ -71,11 +68,38 @@ int cpupri_find(struct cpupri *cp, struct task_struct *p,
         int                  idx      = 0;
         int                  task_pri = convert_prio(p->prio);
 
-        for_each_cpupri_active(cp->pri_active, idx) {
-                struct cpupri_vec *vec  = &cp->pri_to_cpu[idx];
+        if (task_pri >= MAX_RT_PRIO)
+                return 0;
 
-                if (idx >= task_pri)
-                        break;
+        for (idx = 0; idx < task_pri; idx++) {
+                struct cpupri_vec *vec  = &cp->pri_to_cpu[idx];
+                int skip = 0;
+
+                if (!atomic_read(&(vec)->count))
+                        skip = 1;
+                /*
+                 * When looking at the vector, we need to read the counter,
+                 * do a memory barrier, then read the mask.
+                 *
+                 * Note: This is still all racey, but we can deal with it.
+                 *  Ideally, we only want to look at masks that are set.
+                 *
+                 *  If a mask is not set, then the only thing wrong is that we
+                 *  did a little more work than necessary.
+                 *
+                 *  If we read a zero count but the mask is set, because of the
+                 *  memory barriers, that can only happen when the highest prio
+                 *  task for a run queue has left the run queue, in which case,
+                 *  it will be followed by a pull. If the task we are processing
+                 *  fails to find a proper place to go, that pull request will
+                 *  pull this task if the run queue is running at a lower
+                 *  priority.
+                 */
+                smp_rmb();
+
+                /* Need to do the rmb for every iteration */
+                if (skip)
+                        continue;
 
                 if (cpumask_any_and(&p->cpus_allowed, vec->mask) >= nr_cpu_ids)
                         continue;
@@ -115,7 +139,7 @@ void cpupri_set(struct cpupri *cp, int cpu, int newpri)
 {
         int                 *currpri = &cp->cpu_to_pri[cpu];
         int                  oldpri  = *currpri;
-        unsigned long        flags;
+        int                  do_mb = 0;
 
         newpri = convert_prio(newpri);
 
@@ -128,32 +152,46 @@ void cpupri_set(struct cpupri *cp, int cpu, int newpri)
          * If the cpu was currently mapped to a different value, we
          * need to map it to the new value then remove the old value.
          * Note, we must add the new value first, otherwise we risk the
-         * cpu being cleared from pri_active, and this cpu could be
-         * missed for a push or pull.
+         * cpu being missed by the priority loop in cpupri_find.
          */
         if (likely(newpri != CPUPRI_INVALID)) {
                 struct cpupri_vec *vec = &cp->pri_to_cpu[newpri];
 
-                raw_spin_lock_irqsave(&vec->lock, flags);
-
                 cpumask_set_cpu(cpu, vec->mask);
-                vec->count++;
-                if (vec->count == 1)
-                        set_bit(newpri, cp->pri_active);
-
-                raw_spin_unlock_irqrestore(&vec->lock, flags);
+                /*
+                 * When adding a new vector, we update the mask first,
+                 * do a write memory barrier, and then update the count, to
+                 * make sure the vector is visible when count is set.
+                 */
+                smp_mb__before_atomic_inc();
+                atomic_inc(&(vec)->count);
+                do_mb = 1;
         }
         if (likely(oldpri != CPUPRI_INVALID)) {
                 struct cpupri_vec *vec  = &cp->pri_to_cpu[oldpri];
 
-                raw_spin_lock_irqsave(&vec->lock, flags);
-
-                vec->count--;
-                if (!vec->count)
-                        clear_bit(oldpri, cp->pri_active);
+                /*
+                 * Because the order of modification of the vec->count
+                 * is important, we must make sure that the update
+                 * of the new prio is seen before we decrement the
+                 * old prio. This makes sure that the loop sees
+                 * one or the other when we raise the priority of
+                 * the run queue. We don't care about when we lower the
+                 * priority, as that will trigger an rt pull anyway.
+                 *
+                 * We only need to do a memory barrier if we updated
+                 * the new priority vec.
+                 */
+                if (do_mb)
+                        smp_mb__after_atomic_inc();
+
+                /*
+                 * When removing from the vector, we decrement the counter first
+                 * do a memory barrier and then clear the mask.
+                 */
+                atomic_dec(&(vec)->count);
+                smp_mb__after_atomic_inc();
                 cpumask_clear_cpu(cpu, vec->mask);
-
-                raw_spin_unlock_irqrestore(&vec->lock, flags);
         }
 
         *currpri = newpri;
@@ -175,8 +213,7 @@ int cpupri_init(struct cpupri *cp)
         for (i = 0; i < CPUPRI_NR_PRIORITIES; i++) {
                 struct cpupri_vec *vec = &cp->pri_to_cpu[i];
 
-                raw_spin_lock_init(&vec->lock);
-                vec->count = 0;
+                atomic_set(&vec->count, 0);
                 if (!zalloc_cpumask_var(&vec->mask, GFP_KERNEL))
                         goto cleanup;
         }