xen/sched: fix sched_move_domain()

Do cleanup in sched_move_domain() in a dedicated service function,
which is called either in error case with newly allocated data, or in
success case with the old data to be freed.

This will at once fix some subtle bugs which sneaked in due to
forgetting to overwrite some pointers in the error case.

Fixes: 70fadc4163 ("xen/cpupool: support moving domain between cpupools with different granularity")
Reported-by: René Winther Højgaard <renewin@proton.me>
Initial-fix-by: Jan Beulich <jbeulich@suse.com>
Initial-fix-by: George Dunlap <george.dunlap@cloud.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Acked-by: George Dunlap <george.dunlap@cloud.com>

xen/common/sched/core.c

@@ -647,6 +647,24 @@ static void sched_move_irqs(const struct sched_unit *unit)
         vcpu_move_irqs(v);
 }
 
+static void sched_move_domain_cleanup(const struct scheduler *ops,
+                                      struct sched_unit *units,
+                                      void *domdata)
+{
+    struct sched_unit *unit, *old_unit;
+
+    for ( unit = units; unit; )
+    {
+        if ( unit->priv )
+            sched_free_udata(ops, unit->priv);
+        old_unit = unit;
+        unit = unit->next_in_list;
+        xfree(old_unit);
+    }
+
+    sched_free_domdata(ops, domdata);
+}
+
 /*
  * Move a domain from one cpupool to another.
  *
@@ -686,7 +704,6 @@ int sched_move_domain(struct domain *d, struct cpupool *c)
     void *old_domdata;
     unsigned int gran = cpupool_get_granularity(c);
     unsigned int n_units = d->vcpu[0] ? DIV_ROUND_UP(d->max_vcpus, gran) : 0;
-    int ret = 0;
 
     for_each_vcpu ( d, v )
     {
@@ -699,8 +716,9 @@ int sched_move_domain(struct domain *d, struct cpupool *c)
     domdata = sched_alloc_domdata(c->sched, d);
     if ( IS_ERR(domdata) )
     {
-        ret = PTR_ERR(domdata);
-        goto out;
+        rcu_read_unlock(&sched_res_rculock);
+
+        return PTR_ERR(domdata);
     }
 
     for ( unit_idx = 0; unit_idx < n_units; unit_idx++ )
@@ -718,10 +736,10 @@ int sched_move_domain(struct domain *d, struct cpupool *c)
 
         if ( !unit || !unit->priv )
         {
-            old_units = new_units;
-            old_domdata = domdata;
-            ret = -ENOMEM;
-            goto out_free;
+            sched_move_domain_cleanup(c->sched, new_units, domdata);
+            rcu_read_unlock(&sched_res_rculock);
+
+            return -ENOMEM;
         }
 
         unit_ptr = &unit->next_in_list;
@@ -808,22 +826,11 @@ int sched_move_domain(struct domain *d, struct cpupool *c)
 
     domain_unpause(d);
 
- out_free:
-    for ( unit = old_units; unit; )
-    {
-        if ( unit->priv )
-            sched_free_udata(c->sched, unit->priv);
-        old_unit = unit;
-        unit = unit->next_in_list;
-        xfree(old_unit);
-    }
+    sched_move_domain_cleanup(old_ops, old_units, old_domdata);
 
-    sched_free_domdata(old_ops, old_domdata);
-
- out:
     rcu_read_unlock(&sched_res_rculock);
 
-    return ret;
+    return 0;
 }
 
 void sched_destroy_vcpu(struct vcpu *v)