[PATCH] xprtrdam: Don't treat a call as bcall when bc_serv is NULL

[Kinglong Mee <kinglongmee@gmail.com>]

When rdma server returns a fault reply, rpcrdma may treats it as a bcall.
As using NFSv3, a bc server is never exist.
rpcrdma_bc_receive_call will meets NULL pointer as,

[  226.057890] BUG: unable to handle kernel NULL pointer dereference at 
00000000000000c8
...
[  226.058704] RIP: 0010:_raw_spin_lock+0xc/0x20
...
[  226.059732] Call Trace:
[  226.059878]  rpcrdma_bc_receive_call+0x138/0x327 [rpcrdma]
[  226.060011]  __ib_process_cq+0x89/0x170 [ib_core]
[  226.060092]  ib_cq_poll_work+0x26/0x80 [ib_core]
[  226.060257]  process_one_work+0x1a7/0x360
[  226.060367]  ? create_worker+0x1a0/0x1a0
[  226.060440]  worker_thread+0x30/0x390
[  226.060500]  ? create_worker+0x1a0/0x1a0
[  226.060574]  kthread+0x116/0x130
[  226.060661]  ? kthread_flush_work_fn+0x10/0x10
[  226.060724]  ret_from_fork+0x35/0x40
...

Signed-off-by: Kinglong Mee <kinglongmee@gmail.com>
---
  net/sunrpc/xprtrdma/rpc_rdma.c | 5 +++++
  1 file changed, 5 insertions(+)

diff --git a/net/sunrpc/xprtrdma/rpc_rdma.c b/net/sunrpc/xprtrdma/rpc_rdma.c
index 281ddb87ac8d..9486bb98eb2f 100644
--- a/net/sunrpc/xprtrdma/rpc_rdma.c
+++ b/net/sunrpc/xprtrdma/rpc_rdma.c
@@ -1121,9 +1121,14 @@ static bool
  rpcrdma_is_bcall(struct rpcrdma_xprt *r_xprt, struct rpcrdma_rep *rep)
  #if defined(CONFIG_SUNRPC_BACKCHANNEL)
  {
+	struct rpc_xprt *xprt = &r_xprt->rx_xprt;
  	struct xdr_stream *xdr = &rep->rr_stream;
  	__be32 *p;

+	/* no bc service, not a bcall. */
+	if (xprt->bc_serv == NULL)
+		return false;
+
  	if (rep->rr_proc != rdma_msg)
  		return false;

-- 
2.27.0