[xen staging-4.13] sched: fix onlining cpu with core scheduling active

[patchbot@xxxxxxx]

commit 6a5ebbb1fcfa25a4f0aa4c16b4abd63c1e7718bf
Author:     Juergen Gross <jgross@xxxxxxxx>
AuthorDate: Thu Apr 9 09:10:55 2020 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Apr 9 09:10:55 2020 +0200

    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@xxxxxxxx>
    Reviewed-by: Dario Faggioli <dfaggioli@xxxxxxxx>
    master commit: 4c7d340f75abc64f131b0f9bffd6d66d72e43528
    master date: 2020-03-24 17:36:44 +0100
---
 xen/common/cpupool.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/xen/common/cpupool.c b/xen/common/cpupool.c
index 5a90bdc9ff..b90bf42703 100644
--- a/xen/common/cpupool.c
+++ b/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);
--
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