With preemption enabled (CONFIG_DEBUG_PREEMPT=y), the following appeared
when rnbd client tries to map remote block device.

  BUG: using smp_processor_id() in preemptible [00000000] code: bash/1733
  caller is debug_smp_processor_id+0x17/0x20
  CPU: 0 PID: 1733 Comm: bash Not tainted 5.16.0-rc1 #5
  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.14.0-0-g155821a-rebuilt.opensuse.org 04/01/2014
  Call Trace:
   <TASK>
   dump_stack_lvl+0x5d/0x78
   dump_stack+0x10/0x12
   check_preemption_disabled+0xe4/0xf0
   debug_smp_processor_id+0x17/0x20
   rtrs_clt_update_all_stats+0x3b/0x70 [rtrs_client]
   rtrs_clt_read_req+0xc3/0x380 [rtrs_client]
   ? rtrs_clt_init_req+0xe3/0x120 [rtrs_client]
   rtrs_clt_request+0x1a7/0x320 [rtrs_client]
   ? 0xffffffffc0ab1000
   send_usr_msg+0xbf/0x160 [rnbd_client]
   ? rnbd_clt_put_sess+0x60/0x60 [rnbd_client]
   ? send_usr_msg+0x160/0x160 [rnbd_client]
   ? sg_alloc_table+0x27/0xb0
   ? sg_zero_buffer+0xd0/0xd0
   send_msg_sess_info+0xe9/0x180 [rnbd_client]
   ? rnbd_clt_put_sess+0x60/0x60 [rnbd_client]
   ? blk_mq_alloc_tag_set+0x2ef/0x370
   rnbd_clt_map_device+0xba8/0xcd0 [rnbd_client]
   ? send_msg_open+0x200/0x200 [rnbd_client]
   rnbd_clt_map_device_store+0x3e5/0x620 [rnbd_client

To supress the calltrace, let's call get_cpu_ptr/put_cpu_ptr pair in
rtrs_clt_update_rdma_stats to disable preemption when accessing per-cpu
variable.

While at it, let's make the similar change in rtrs_clt_update_wc_stats.
And for rtrs_clt_inc_failover_cnt, though it was only called inside rcu
section, but it still can be preempted in case CONFIG_PREEMPT_RCU is
enabled, so change it to {get,put}_cpu_ptr pair either.

Link: https://lore.kernel.org/r/20211128133501.38710-1-guoqing.jiang@linux.devSigned-off-by: NGuoqing Jiang <guoqing.jiang@linux.dev>
Reviewed-by: NLeon Romanovsky <leonro@nvidia.com>
Signed-off-by: NJason Gunthorpe <jgg@nvidia.com>