xen: credit2: never consider CPUs outside of our cpupool.

In fact, relying on the mask of what pCPUs belong to
which Credit2 runqueue is not enough. If we only do that,
when Credit2 is the boot scheduler, we may ASSERT() or
panic when moving a pCPU from Pool-0 to another cpupool.

This is because pCPUs outside of any pool are considered
part of cpupool0. This puts us at risk of crash when those
same pCPUs are added to another pool and something
different than the idle domain is found to be running
on them.

Note that, even if we prevent the above to happen (which
is the purpose of this patch), this is still pretty bad,
in fact, when we remove a pCPU from Pool-0:
- in Credit1, as we do *not* update prv->ncpus and
  prv->credit, which means we're considering the wrong
  total credits when doing accounting;
- in Credit2, the pCPU remains part of one runqueue,
  and is hence at least considered during load balancing,
  even if no vCPU should really run there.

In Credit1, this "only" causes skewed accounting and
no crashes because there is a lot of `cpumask_and`ing
going on with the cpumask of the domains' cpupool
(which, BTW, comes at a price).

A quick and not to involved (and easily backportable)
solution for Credit2, is to do exactly the same.

Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com
Acked-by: George Dunlap <george.dunlap@citrix.com>

diff --git a/xen/common/sched_credit2.c b/xen/common/sched_credit2.c
index 523922ee95b40d4a433eaea4aba12235f7c1d851..ce0e14624195a0f51235ee894200893f54605e65 100644 (file)
--- a/xen/common/sched_credit2.c
+++ b/xen/common/sched_credit2.c
@@ -510,19 +510,22 @@ void smt_idle_mask_clear(unsigned int cpu, cpumask_t *mask)
  */
 static int get_fallback_cpu(struct csched2_vcpu *svc)
 {
-    int fallback_cpu, cpu = svc->vcpu->processor;
+    struct vcpu *v = svc->vcpu;
+    int cpu = v->processor;
 
-    if ( likely(cpumask_test_cpu(cpu, svc->vcpu->cpu_hard_affinity)) )
-        return cpu;
+    cpumask_and(cpumask_scratch_cpu(cpu), v->cpu_hard_affinity,
+                cpupool_domain_cpumask(v->domain));
 
-    cpumask_and(cpumask_scratch_cpu(cpu), svc->vcpu->cpu_hard_affinity,
-                &svc->rqd->active);
-    fallback_cpu = cpumask_first(cpumask_scratch_cpu(cpu));
-    if ( likely(fallback_cpu < nr_cpu_ids) )
-        return fallback_cpu;
+    if ( likely(cpumask_test_cpu(cpu, cpumask_scratch_cpu(cpu))) )
+        return cpu;
 
-    cpumask_and(cpumask_scratch, svc->vcpu->cpu_hard_affinity,
-                cpupool_domain_cpumask(svc->vcpu->domain));
+    if ( likely(cpumask_intersects(cpumask_scratch_cpu(cpu),
+                                   &svc->rqd->active)) )
+    {
+        cpumask_and(cpumask_scratch_cpu(cpu), &svc->rqd->active,
+                    cpumask_scratch_cpu(cpu));
+        return cpumask_first(cpumask_scratch_cpu(cpu));
+    }
 
     ASSERT(!cpumask_empty(cpumask_scratch_cpu(cpu)));
 
@@ -940,6 +943,9 @@ runq_tickle(const struct scheduler *ops, struct csched2_vcpu *new, s_time_t now)
                     (unsigned char *)&d);
     }
 
+    cpumask_and(cpumask_scratch_cpu(cpu), new->vcpu->cpu_hard_affinity,
+                cpupool_domain_cpumask(new->vcpu->domain));
+
     /*
      * First of all, consider idle cpus, checking if we can just
      * re-use the pcpu where we were running before.
@@ -952,7 +958,7 @@ runq_tickle(const struct scheduler *ops, struct csched2_vcpu *new, s_time_t now)
         cpumask_andnot(&mask, &rqd->idle, &rqd->smt_idle);
     else
         cpumask_copy(&mask, &rqd->smt_idle);
-    cpumask_and(&mask, &mask, new->vcpu->cpu_hard_affinity);
+    cpumask_and(&mask, &mask, cpumask_scratch_cpu(cpu));
     i = cpumask_test_or_cycle(cpu, &mask);
     if ( i < nr_cpu_ids )
     {
@@ -967,7 +973,7 @@ runq_tickle(const struct scheduler *ops, struct csched2_vcpu *new, s_time_t now)
      * gone through the scheduler yet.
      */
     cpumask_andnot(&mask, &rqd->idle, &rqd->tickled);
-    cpumask_and(&mask, &mask, new->vcpu->cpu_hard_affinity);
+    cpumask_and(&mask, &mask, cpumask_scratch_cpu(cpu));
     i = cpumask_test_or_cycle(cpu, &mask);
     if ( i < nr_cpu_ids )
     {
@@ -983,7 +989,7 @@ runq_tickle(const struct scheduler *ops, struct csched2_vcpu *new, s_time_t now)
      */
     cpumask_andnot(&mask, &rqd->active, &rqd->idle);
     cpumask_andnot(&mask, &mask, &rqd->tickled);
-    cpumask_and(&mask, &mask, new->vcpu->cpu_hard_affinity);
+    cpumask_and(&mask, &mask, cpumask_scratch_cpu(cpu));
     if ( cpumask_test_cpu(cpu, &mask) )
     {
         cur = CSCHED2_VCPU(curr_on_cpu(cpu));
@@ -1525,6 +1531,9 @@ csched2_cpu_pick(const struct scheduler *ops, struct vcpu *vc)
         goto out;
     }
 
+    cpumask_and(cpumask_scratch_cpu(cpu), vc->cpu_hard_affinity,
+                cpupool_domain_cpumask(vc->domain));
+
     /*
      * First check to see if we're here because someone else suggested a place
      * for us to move.
@@ -1536,13 +1545,13 @@ csched2_cpu_pick(const struct scheduler *ops, struct vcpu *vc)
             printk(XENLOG_WARNING "%s: target runqueue disappeared!\n",
                    __func__);
         }
-        else
+        else if ( cpumask_intersects(cpumask_scratch_cpu(cpu),
+                                     &svc->migrate_rqd->active) )
         {
-            cpumask_and(cpumask_scratch_cpu(cpu), vc->cpu_hard_affinity,
+            cpumask_and(cpumask_scratch_cpu(cpu), cpumask_scratch_cpu(cpu),
                         &svc->migrate_rqd->active);
             new_cpu = cpumask_any(cpumask_scratch_cpu(cpu));
-            if ( new_cpu < nr_cpu_ids )
-                goto out_up;
+            goto out_up;
         }
         /* Fall-through to normal cpu pick */
     }
@@ -1570,12 +1579,12 @@ csched2_cpu_pick(const struct scheduler *ops, struct vcpu *vc)
          */
         if ( rqd == svc->rqd )
         {
-            if ( cpumask_intersects(vc->cpu_hard_affinity, &rqd->active) )
+            if ( cpumask_intersects(cpumask_scratch_cpu(cpu), &rqd->active) )
                 rqd_avgload = max_t(s_time_t, rqd->b_avgload - svc->avgload, 0);
         }
         else if ( spin_trylock(&rqd->lock) )
         {
-            if ( cpumask_intersects(vc->cpu_hard_affinity, &rqd->active) )
+            if ( cpumask_intersects(cpumask_scratch_cpu(cpu), &rqd->active) )
                 rqd_avgload = rqd->b_avgload;
 
             spin_unlock(&rqd->lock);
@@ -1597,7 +1606,7 @@ csched2_cpu_pick(const struct scheduler *ops, struct vcpu *vc)
         goto out_up;
     }
 
-    cpumask_and(cpumask_scratch_cpu(cpu), vc->cpu_hard_affinity,
+    cpumask_and(cpumask_scratch_cpu(cpu), cpumask_scratch_cpu(cpu),
                 &prv->rqd[min_rqi].active);
     new_cpu = cpumask_any(cpumask_scratch_cpu(cpu));
     BUG_ON(new_cpu >= nr_cpu_ids);
@@ -1713,6 +1722,8 @@ static void migrate(const struct scheduler *ops,
         __runq_deassign(svc);
 
         cpumask_and(cpumask_scratch_cpu(cpu), svc->vcpu->cpu_hard_affinity,
+                    cpupool_domain_cpumask(svc->vcpu->domain));
+        cpumask_and(cpumask_scratch_cpu(cpu), cpumask_scratch_cpu(cpu),
                     &trqd->active);
         svc->vcpu->processor = cpumask_any(cpumask_scratch_cpu(cpu));
         ASSERT(svc->vcpu->processor < nr_cpu_ids);
@@ -1738,8 +1749,14 @@ static void migrate(const struct scheduler *ops,
 static bool_t vcpu_is_migrateable(struct csched2_vcpu *svc,
                                   struct csched2_runqueue_data *rqd)
 {
+    struct vcpu *v = svc->vcpu;
+    int cpu = svc->vcpu->processor;
+
+    cpumask_and(cpumask_scratch_cpu(cpu), v->cpu_hard_affinity,
+                cpupool_domain_cpumask(v->domain));
+
     return !(svc->flags & CSFLAG_runq_migrate_request) &&
-           cpumask_intersects(svc->vcpu->cpu_hard_affinity, &rqd->active);
+           cpumask_intersects(cpumask_scratch_cpu(cpu), &rqd->active);
 }
 
 static void balance_load(const struct scheduler *ops, int cpu, s_time_t now)