bpf, cpumap: Handle skb as well when clean up ptr_ring

The following warning was reported when running xdp_redirect_cpu with
both skb-mode and stress-mode enabled:

  ------------[ cut here ]------------
  Incorrect XDP memory type (-2128176192) usage
  WARNING: CPU: 7 PID: 1442 at net/core/xdp.c:405
  Modules linked in:
  CPU: 7 PID: 1442 Comm: kworker/7:0 Tainted: G  6.5.0-rc2+ #1
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996)
  Workqueue: events __cpu_map_entry_free
  RIP: 0010:__xdp_return+0x1e4/0x4a0
  ......
  Call Trace:
   <TASK>
   ? show_regs+0x65/0x70
   ? __warn+0xa5/0x240
   ? __xdp_return+0x1e4/0x4a0
   ......
   xdp_return_frame+0x4d/0x150
   __cpu_map_entry_free+0xf9/0x230
   process_one_work+0x6b0/0xb80
   worker_thread+0x96/0x720
   kthread+0x1a5/0x1f0
   ret_from_fork+0x3a/0x70
   ret_from_fork_asm+0x1b/0x30
   </TASK>

The reason for the warning is twofold. One is due to the kthread
cpu_map_kthread_run() is stopped prematurely. Another one is
__cpu_map_ring_cleanup() doesn't handle skb mode and treats skbs in
ptr_ring as XDP frames.

Prematurely-stopped kthread will be fixed by the preceding patch and
ptr_ring will be empty when __cpu_map_ring_cleanup() is called. But
as the comments in __cpu_map_ring_cleanup() said, handling and freeing
skbs in ptr_ring as well to "catch any broken behaviour gracefully".

Fixes: 11941f8a ("bpf: cpumap: Implement generic cpumap")
Signed-off-by: Hou Tao <houtao1@huawei.com>
Acked-by: Jesper Dangaard Brouer <hawk@kernel.org>
Link: https://lore.kernel.org/r/20230729095107.1722450-3-houtao@huaweicloud.com


Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>