sched: Fix null pointer derefrence for sd->span

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I7HFZV


CVE: NA

----------------------------------------

There may be NULL pointer derefrence when hotplug running and
creating taskgroup concurrently.

sched_autogroup_create_attach
  -> sched_create_group
    -> alloc_fair_sched_group
      -> init_auto_affinity
        -> init_affinity_domains
           -> cpumask_copy(xx, sched_domain_span(tmp))
              { tmp may be free due rcu lock missing }

{ hotplug will rebuild sched domain }
sched_cpu_activate
  -> build_sched_domains
    -> cpuset_cpu_active
      -> partition_sched_domains
        -> build_sched_domains
          -> cpu_attach_domain
            -> destroy_sched_domains
              -> call_rcu(&sd->rcu, destroy_sched_domains_rcu)

So sd should be protect with rcu lock in entire critical zone.

[  599.811593] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
[  600.112821] pc : init_affinity_domains+0xf4/0x200
[  600.125918] lr : init_affinity_domains+0xd4/0x200
[  600.331355] Call trace:
[  600.338734]  init_affinity_domains+0xf4/0x200
[  600.347955]  init_auto_affinity+0x78/0xc0
[  600.356622]  alloc_fair_sched_group+0xd8/0x210
[  600.365594]  sched_create_group+0x48/0xc0
[  600.373970]  sched_autogroup_create_attach+0x54/0x190
[  600.383311]  ksys_setsid+0x110/0x130
[  600.391014]  __arm64_sys_setsid+0x18/0x24
[  600.399156]  el0_svc_common+0x118/0x170
[  600.406818]  el0_svc_handler+0x3c/0x80
[  600.414188]  el0_svc+0x8/0x640
[  600.420719] Code: b40002c0 9104e002 f9402061 a9401444 (a9001424)
[  600.430504] SMP: stopping secondary CPUs
[  600.441751] Starting crashdump kernel...

Fixes: 713cfd26 ("sched: Introduce smart grid scheduling strategy for cfs")
Signed-off-by: Hui Tang <tanghui20@huawei.com>
Reviewed-by: Zhang Qiao <zhangqiao22@huawei.com>
Signed-off-by: Zhang Changzhong <zhangchangzhong@huawei.com>
Signed-off-by: Yipeng Zou <zouyipeng@huawei.com>