[PATCH v4 02/10] xprtrdma: xprt_rdma_free() must not release backchannel reqs

[Chuck Lever <chuck.lever@oracle.com>]

Preserve any rpcrdma_req that is attached to rpc_rqst's allocated
for the backchannel. Otherwise, after all the pre-allocated
backchannel req's are consumed, incoming backward calls start
writing on freed memory.

Somehow this hunk got lost.

Fixes: f531a5dbc451 ('xprtrdma: Pre-allocate backward rpc_rqst')
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: Devesh Sharma <devesh.sharma@avagotech.com>
---
 net/sunrpc/xprtrdma/transport.c |    3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/sunrpc/xprtrdma/transport.c b/net/sunrpc/xprtrdma/transport.c
index 8c545f7..740bddc 100644
--- a/net/sunrpc/xprtrdma/transport.c
+++ b/net/sunrpc/xprtrdma/transport.c
@@ -576,6 +576,9 @@ xprt_rdma_free(void *buffer)
 
 	rb = container_of(buffer, struct rpcrdma_regbuf, rg_base[0]);
 	req = rb->rg_owner;
+	if (req->rl_backchannel)
+		return;
+
 	r_xprt = container_of(req->rl_buffer, struct rpcrdma_xprt, rx_buf);
 
 	dprintk("RPC:       %s: called on 0x%p\n", __func__, req->rl_reply);