[PATCH v1 08/20] xprtrdma: Reply buffer exhaustion can be catastrophic

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

Not having an rpcrdma_rep at call_allocate time can be a problem.
It means that send_request can't post a receive buffer to catch
the RPC's reply. Possible consequences are deadlock or RPC
timeouts.

Instead of allowing an RPC to proceed if an rpcrdma_rep is
not available, return NULL to force call_allocate to wait and
try again.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 net/sunrpc/xprtrdma/verbs.c |    6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
index 4867923..e016b9c 100644
--- a/net/sunrpc/xprtrdma/verbs.c
+++ b/net/sunrpc/xprtrdma/verbs.c
@@ -1009,8 +1009,6 @@ rpcrdma_put_mw(struct rpcrdma_xprt *r_xprt, struct rpcrdma_mw *mw)
 
 /*
  * Get a set of request/reply buffers.
- *
- * Reply buffer (if available) is attached to send buffer upon return.
  */
 struct rpcrdma_req *
 rpcrdma_buffer_get(struct rpcrdma_buffer *buffers)
@@ -1032,10 +1030,10 @@ out_reqbuf:
 	pr_warn("RPC:       %s: out of request buffers\n", __func__);
 	return NULL;
 out_repbuf:
+	list_add(&req->rl_free, &buffers->rb_send_bufs);
 	spin_unlock(&buffers->rb_lock);
 	pr_warn("RPC:       %s: out of reply buffers\n", __func__);
-	req->rl_reply = NULL;
-	return req;
+	return NULL;
 }
 
 /*