[PATCH 2/4] RDMA/rxe: Fix dead lock caused by rxe_alloc interrupted by rxe_pool_get_index

[yanjun.zhu@xxxxxxxxx]

From: Zhu Yanjun <yanjun.zhu@xxxxxxxxx>

The ah_pool xa_lock first is acquired in this:

{SOFTIRQ-ON-W} state was registered at:
  lock_acquire+0x1d2/0x5a0
  _raw_spin_lock+0x33/0x80
  rxe_alloc+0x1be/0x290 [rdma_rxe]

Then ah_pool xa_lock is acquired in this:

{IN-SOFTIRQ-W}:
  <TASK>
  __lock_acquire+0x1565/0x34a0
  lock_acquire+0x1d2/0x5a0
  _raw_spin_lock_irqsave+0x42/0x90
  rxe_pool_get_index+0x72/0x1d0 [rdma_rxe]
  </TASK>