sched: fix onlining cpu with core scheduling active

When onlining a cpu cpupool_cpu_add() checks whether all siblings of
the new cpu are free in order to decide whether to add it to cpupool0.
In case the added cpu is not the last sibling to be onlined this test
is wrong as it only checks for all online siblings to be free. The
test should include the check for the number of siblings having
reached the scheduling granularity of cpupool0, too.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Dario Faggioli <dfaggioli@suse.com>
master commit: 4c7d340f75
master date: 2020-03-24 17:36:44 +0100

xen/common/cpupool.c

@@ -615,7 +615,8 @@ static int cpupool_cpu_add(unsigned int cpu)
     get_sched_res(cpu)->cpupool = NULL;
 
     cpus = sched_get_opt_cpumask(cpupool0->gran, cpu);
-    if ( cpumask_subset(cpus, &cpupool_free_cpus) )
+    if ( cpumask_subset(cpus, &cpupool_free_cpus) &&
+         cpumask_weight(cpus) == cpupool_get_granularity(cpupool0) )
         ret = cpupool_assign_cpu_locked(cpupool0, cpu);
 
     rcu_read_unlock(&sched_res_rculock);