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: 132cbe8f35 ("sched: fix get_cpu_idle_time() with core scheduling")
Reported-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Tested-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Dario Faggioli <dfaggioli@suse.com>
master commit: 5293470a77
master date: 2021-08-19 13:38:31 +0200

xen/common/schedule.c

@@ -334,7 +334,7 @@ uint64_t get_cpu_idle_time(unsigned int cpu)
     struct vcpu_runstate_info state = { 0 };
     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];