The following warning was reported when running "./test_progs -t
test_bpf_ma/percpu_free_through_map_free":

  ------------[ cut here ]------------
  WARNING: CPU: 1 PID: 68 at kernel/bpf/memalloc.c:342
  CPU: 1 PID: 68 Comm: kworker/u16:2 Not tainted 6.6.0-rc2+ #222
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996)
  Workqueue: events_unbound bpf_map_free_deferred
  RIP: 0010:bpf_mem_refill+0x21c/0x2a0
  ......
  Call Trace:
   <IRQ>
   ? bpf_mem_refill+0x21c/0x2a0
   irq_work_single+0x27/0x70
   irq_work_run_list+0x2a/0x40
   irq_work_run+0x18/0x40
   __sysvec_irq_work+0x1c/0xc0
   sysvec_irq_work+0x73/0x90
   </IRQ>
   <TASK>
   asm_sysvec_irq_work+0x1b/0x20
  RIP: 0010:unit_free+0x50/0x80
   ......
   bpf_mem_free+0x46/0x60
   __bpf_obj_drop_impl+0x40/0x90
   bpf_obj_free_fields+0x17d/0x1a0
   array_map_free+0x6b/0x170
   bpf_map_free_deferred+0x54/0xa0
   process_scheduled_works+0xba/0x370
   worker_thread+0x16d/0x2e0
   kthread+0x105/0x140
   ret_from_fork+0x39/0x60
   ret_from_fork_asm+0x1b/0x30
   </TASK>
  ---[ end trace 0000000000000000 ]---

The reason is simple: __bpf_obj_drop_impl() does not know the freeing
field is a per-cpu pointer and it uses bpf_global_ma to free the
pointer. Because bpf_global_ma is not a per-cpu allocator, so ksize() is
used to select the corresponding cache. The bpf_mem_cache with 16-bytes
unit_size will always be selected to do the unmatched free and it will
trigger the warning in free_bulk() eventually.

Because per-cpu kptr doesn't support list or rb-tree now, so fix the
problem by only checking whether or not the type of kptr is per-cpu in
bpf_obj_free_fields(), and using bpf_global_percpu_ma to these kptrs.
Signed-off-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/r/20231020133202.4043247-7-houtao@huaweicloud.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>