sched: Fix potential NULL derference of doms_cur

If CONFIG_CPUMASK_OFFSTACK is enabled but doms_cur alloc failed in
arch_init_sched_domains(), doms_cur will move back to
fallback_doms. But this time, fallback_doms has not been
initialized yet.

Signed-off-by: Yong Zhang <[email protected]>
Cc: [email protected]
LKML-Reference: <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>

kernel/sched.c

@@ -9165,6 +9165,7 @@ void __init sched_init_smp(void)
 	cpumask_var_t non_isolated_cpus;
 
 	alloc_cpumask_var(&non_isolated_cpus, GFP_KERNEL);
+	alloc_cpumask_var(&fallback_doms, GFP_KERNEL);
 
 #if defined(CONFIG_NUMA)
 	sched_group_nodes_bycpu = kzalloc(nr_cpu_ids * sizeof(void **),
@@ -9196,7 +9197,6 @@ void __init sched_init_smp(void)
 	sched_init_granularity();
 	free_cpumask_var(non_isolated_cpus);
 
-	alloc_cpumask_var(&fallback_doms, GFP_KERNEL);
 	init_sched_rt_class();
 }
 #else