svcrdma: fix miss destroy percpu_counter in svc_rdma_proc_init()

In the Linux kernel, the following vulnerability has been resolved: svcrdma: fix miss destroy percpu_counter in svc_rdma_proc_init() There's issue as follows: RPC: Registered rdma transport module. RPC: Registered rdma backchannel transport module. RPC: Unregistered rdma transport module. RPC: Unregistered rdma backchannel transport module. BUG: unable to handle page fault for address: fffffbfff80c609a PGD 123fee067 P4D 123fee067 PUD 123fea067 PMD 10c624067 PTE 0 Oops: Oops: 0000 [#1] PREEMPT SMP KASAN NOPTI RIP: 0010:percpu_counter_destroy_many+0xf7/0x2a0 Call Trace: <TASK> __die+0x1f/0x70 page_fault_oops+0x2cd/0x860 spurious_kernel_fault+0x36/0x450 do_kern_addr_fault+0xca/0x100 exc_page_fault+0x128/0x150 asm_exc_page_fault+0x26/0x30 percpu_counter_destroy_many+0xf7/0x2a0 mmdrop+0x209/0x350 finish_task_switch.isra.0+0x481/0x840 schedule_tail+0xe/0xd0 ret_from_fork+0x23/0x80 ret_from_fork_asm+0x1a/0x30 </TASK> If register_sysctl() return NULL, then svc_rdma_proc_cleanup() will not destroy the percpu counters which init in svc_rdma_proc_init(). If CONFIG_HOTPLUG_CPU is enabled, residual nodes may be in the 'percpu_counters' list. The above issue may occur once the module is removed. If the CONFIG_HOTPLUG_CPU configuration is not enabled, memory leakage occurs. To solve above issue just destroy all percpu counters when register_sysctl() return NULL.