Mellanox ConnectX-4 (mlx5) used for SCSI RDMA Protocol (SRP) is exposed to lock contention in srp_queuecommand(), srp_recv_completion(), mlx5_ib_poll_cq()

Issue

• While using Mellanox ConnectX-4 (mlx5 driver) to access SCSI RDMA Protocol (SRP) devices hard lockups have been seen during IO loading. The logged call trace output of course varies, but the most common paths documented to have seen the problem include

  • srp_recv_completion()
  • srp_queuecommand()
  • srp_send_completion()

• The same issue has also surfaced in __list_add(), with the following in the logs

  BUG: unable to handle kernel NULL pointer dereference at 0000000000000002
  IP: [<ffffffff8130c2c3>] __list_add+0x33/0xc0
  Oops: 0002 [#1] SMP