[xen staging] cpupool: fix removing cpu from a cpupool

[patchbot@xxxxxxx]

commit 498d73647fa17d9eb7a67d2e9bdccac6b438e559
Author:     Juergen Gross <jgross@xxxxxxxx>
AuthorDate: Fri May 8 10:44:22 2020 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri May 8 10:44:22 2020 +0200

    cpupool: fix removing cpu from a cpupool
    
    Commit cb563d7665f2 ("xen/sched: support core scheduling for moving
    cpus to/from cpupools") introduced a regression when trying to remove
    an offline cpu from a cpupool, as the system would crash in this
    situation.
    
    Fix that by testing the cpu to be online.
    
    Fixes: cb563d7665f2 ("xen/sched: support core scheduling for moving cpus 
to/from cpupools")
    Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
    Acked-by: Dario Faggioli <dfaggioli@xxxxxxxx>
---
 xen/common/sched/cpupool.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/xen/common/sched/cpupool.c b/xen/common/sched/cpupool.c
index 97c2d5b3c1..0664f7fa3d 100644
--- a/xen/common/sched/cpupool.c
+++ b/xen/common/sched/cpupool.c
@@ -552,6 +552,9 @@ static int cpupool_unassign_cpu(struct cpupool *c, unsigned 
int cpu)
     debugtrace_printk("cpupool_unassign_cpu(pool=%d,cpu=%d)\n",
                       c->cpupool_id, cpu);
 
+    if ( !cpu_online(cpu) )
+        return -EINVAL;
+
     master_cpu = sched_get_resource_cpu(cpu);
     ret = cpupool_unassign_cpu_start(c, master_cpu);
     if ( ret )
--
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