[xen stable-4.15] xen/sched: fix get_cpu_idle_time() for smt=0 suspend/resume

[patchbot@xxxxxxx]

commit b654bb2ed2f35339ab03966e5dd64cf341cec8b1
Author:     Juergen Gross <jgross@xxxxxxxx>
AuthorDate: Wed Aug 25 14:50:43 2021 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Aug 25 14:50:43 2021 +0200

    xen/sched: fix get_cpu_idle_time() for smt=0 suspend/resume
    
    With smt=0 during a suspend/resume cycle of the machine the threads
    which have been parked before will briefly come up again. This can
    result in problems e.g. with cpufreq driver being active as this will
    call into get_cpu_idle_time() for a cpu without initialized scheduler
    data.
    
    Fix that by letting get_cpu_idle_time() deal with this case. Drop a
    redundant check in exchange.
    
    Fixes: 132cbe8f35632fb2 ("sched: fix get_cpu_idle_time() with core 
scheduling")
    Reported-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
    Tested-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Dario Faggioli <dfaggioli@xxxxxxxx>
    master commit: 5293470a77ad980dce2af9b7e6c3f11eeebf1b64
    master date: 2021-08-19 13:38:31 +0200
---
 xen/common/sched/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/common/sched/core.c b/xen/common/sched/core.c
index 6d34764d38..8d178baf3d 100644
--- a/xen/common/sched/core.c
+++ b/xen/common/sched/core.c
@@ -337,7 +337,7 @@ uint64_t get_cpu_idle_time(unsigned int cpu)
     struct vcpu_runstate_info state = { 0 };
     const struct vcpu *v = idle_vcpu[cpu];
 
-    if ( cpu_online(cpu) && v )
+    if ( cpu_online(cpu) && get_sched_res(cpu) )
         vcpu_runstate_get(v, &state);
 
     return state.time[RUNSTATE_running];
--
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