[Xen-changelog] [xen stable-4.8] xen: credit2: never consider CPUs outside of our cpupool.

[patchbot@xxxxxxx]

commit a20300baf5714ed6098a4068e0f464d6971fe0a7
Author:     Dario Faggioli <dario.faggioli@xxxxxxxxxx>
AuthorDate: Thu Feb 9 10:24:56 2017 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Feb 9 10:24:56 2017 +0100

    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@xxxxxxxxxx
    Acked-by: George Dunlap <george.dunlap@xxxxxxxxxx>
    master commit: e7191920261d20e52ca4c06a03589a1155981b04
    master date: 2017-01-24 17:02:07 +0000
---
 xen/common/sched_credit2.c | 59 +++++++++++++++++++++++++++++-----------------
 1 file changed, 38 insertions(+), 21 deletions(-)

diff --git a/xen/common/sched_credit2.c b/xen/common/sched_credit2.c
index 523922e..ce0e146 100644
--- 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)
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.8

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