After modifying the QP to the Error state, all RX WR would be completed
with WC in IB_WC_WR_FLUSH_ERR status. Current implementation does not
wait for it is done, but destroy the QP and free the link group directly.
So there is a risk that accessing the freed memory in tasklet context.

Here is a crash example:

 BUG: unable to handle page fault for address: ffffffff8f220860
 #PF: supervisor write access in kernel mode
 #PF: error_code(0x0002) - not-present page
 PGD f7300e067 P4D f7300e067 PUD f7300f063 PMD 8c4e45063 PTE 800ffff08c9df060
 Oops: 0002 [#1] SMP PTI
 CPU: 1 PID: 0 Comm: swapper/1 Kdump: loaded Tainted: G S         OE     5.10.0-0607+ #23
 Hardware name: Inspur NF5280M4/YZMB-00689-101, BIOS 4.1.20 07/09/2018
 RIP: 0010:native_queued_spin_lock_slowpath+0x176/0x1b0
 Code: f3 90 48 8b 32 48 85 f6 74 f6 eb d5 c1 ee 12 83 e0 03 83 ee 01 48 c1 e0 05 48 63 f6 48 05 00 c8 02 00 48 03 04 f5 00 09 98 8e <48> 89 10 8b 42 08 85 c0 75 09 f3 90 8b 42 08 85 c0 74 f7 48 8b 32
 RSP: 0018:ffffb3b6c001ebd8 EFLAGS: 00010086
 RAX: ffffffff8f220860 RBX: 0000000000000246 RCX: 0000000000080000
 RDX: ffff91db1f86c800 RSI: 000000000000173c RDI: ffff91db62bace00
 RBP: ffff91db62bacc00 R08: 0000000000000000 R09: c00000010000028b
 R10: 0000000000055198 R11: ffffb3b6c001ea58 R12: ffff91db80e05010
 R13: 000000000000000a R14: 0000000000000006 R15: 0000000000000040
 FS:  0000000000000000(0000) GS:ffff91db1f840000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: ffffffff8f220860 CR3: 00000001f9580004 CR4: 00000000003706e0
 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
 Call Trace:
  <IRQ>
  _raw_spin_lock_irqsave+0x30/0x40
  mlx5_ib_poll_cq+0x4c/0xc50 [mlx5_ib]
  smc_wr_rx_tasklet_fn+0x56/0xa0 [smc]
  tasklet_action_common.isra.21+0x66/0x100
  __do_softirq+0xd5/0x29c
  asm_call_irq_on_stack+0x12/0x20
  </IRQ>
  do_softirq_own_stack+0x37/0x40
  irq_exit_rcu+0x9d/0xa0
  sysvec_call_function_single+0x34/0x80
  asm_sysvec_call_function_single+0x12/0x20

Fixes: bd4ad577 ("smc: initialize IB transport incl. PD, MR, QP, CQ, event, WR")
Signed-off-by: Yacan Liu <liuyacan@corp.netease.com>
Reviewed-by: Tony Lu <tonylu@linux.alibaba.com>
Signed-off-by: David S. Miller <davem@davemloft.net>