RDMA/rtrs: Call {get,put}_cpu_ptr to silence a debug kernel warning

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/[e-mail]
Signed-off-by: Guoqing Jiang <[e-mail]>
Reviewed-by: Leon Romanovsky <[e-mail]>
Signed-off-by: Jason Gunthorpe <[e-mail]>

drivers/infiniband/ulp/rtrs/rtrs-clt-stats.c

···
 	int cpu;
 
 	cpu = raw_smp_processor_id();
-	s = this_cpu_ptr(stats->pcpu_stats);
+	s = get_cpu_ptr(stats->pcpu_stats);
 	if (con->cpu != cpu) {
 		s->cpu_migr.to++;
 
···
 		s = per_cpu_ptr(stats->pcpu_stats, con->cpu);
 		atomic_inc(&s->cpu_migr.from);
 	}
+	put_cpu_ptr(stats->pcpu_stats);
 }
 
 void rtrs_clt_inc_failover_cnt(struct rtrs_clt_stats *stats)
 {
 	struct rtrs_clt_stats_pcpu *s;
 
-	s = this_cpu_ptr(stats->pcpu_stats);
+	s = get_cpu_ptr(stats->pcpu_stats);
 	s->rdma.failover_cnt++;
+	put_cpu_ptr(stats->pcpu_stats);
 }
 
 int rtrs_clt_stats_migration_from_cnt_to_str(struct rtrs_clt_stats *stats, char *buf)
···
 {
 	struct rtrs_clt_stats_pcpu *s;
 
-	s = this_cpu_ptr(stats->pcpu_stats);
+	s = get_cpu_ptr(stats->pcpu_stats);
 	s->rdma.dir[d].cnt++;
 	s->rdma.dir[d].size_total += size;
+	put_cpu_ptr(stats->pcpu_stats);
 }
 
 void rtrs_clt_update_all_stats(struct rtrs_clt_io_req *req, int dir)