xprtrdma: xprt_release_rqst_cong is called outside of transport_lock

chucklever · amschuma-ntap · commit 91ca18660e19 · 2018-10-02T15:26:30.000-04:00
Since commit ce7c252 ("SUNRPC: Add a separate spinlock to protect the RPC request receive list") the RPC/RDMA reply handler has been calling xprt_release_rqst_cong without holding xprt->transport_lock. I think the only way this call is ever made is if the credit grant increases and there are RPCs pending. Current server implementations do not change their credit grant during operation (except at connect time). Commit e7ce710 ("xprtrdma: Avoid deadlock when credit window is reset") added the ->release_rqst call because UDP invokes xprt_adjust_cwnd(), which calls __xprt_put_cong() after adjusting xprt->cwnd. Both xprt_release() and ->xprt_release_xprt already wake another task in this case, so it is safe to remove this call from the reply handler. Signed-off-by: Chuck Lever <chuck.lever@oracle.com> Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
diff --git a/net/sunrpc/xprtrdma/rpc_rdma.c b/net/sunrpc/xprtrdma/rpc_rdma.c
@@ -1216,7 +1216,6 @@ void rpcrdma_complete_rqst(struct rpcrdma_rep *rep)
 	struct rpcrdma_xprt *r_xprt = rep->rr_rxprt;
 	struct rpc_xprt *xprt = &r_xprt->rx_xprt;
 	struct rpc_rqst *rqst = rep->rr_rqst;
-	unsigned long cwnd;
 	int status;
 
 	xprt->reestablish_timeout = 0;
@@ -1239,11 +1238,6 @@ void rpcrdma_complete_rqst(struct rpcrdma_rep *rep)
 
 out:
 	spin_lock(&xprt->recv_lock);
-	cwnd = xprt->cwnd;
-	xprt->cwnd = r_xprt->rx_buf.rb_credits << RPC_CWNDSHIFT;
-	if (xprt->cwnd > cwnd)
-		xprt_release_rqst_cong(rqst->rq_task);
-
 	xprt_complete_rqst(rqst->rq_task, status);
 	xprt_unpin_rqst(rqst);
 	spin_unlock(&xprt->recv_lock);
@@ -1350,14 +1344,18 @@ void rpcrdma_reply_handler(struct rpcrdma_rep *rep)
 	if (!rqst)
 		goto out_norqst;
 	xprt_pin_rqst(rqst);
+	spin_unlock(&xprt->recv_lock);
 
 	if (credits == 0)
 		credits = 1;	/* don't deadlock */
 	else if (credits > buf->rb_max_requests)
 		credits = buf->rb_max_requests;
-	buf->rb_credits = credits;
-
-	spin_unlock(&xprt->recv_lock);
+	if (buf->rb_credits != credits) {
+		spin_lock_bh(&xprt->transport_lock);
+		buf->rb_credits = credits;
+		xprt->cwnd = credits << RPC_CWNDSHIFT;
+		spin_unlock_bh(&xprt->transport_lock);
+	}
 
 	req = rpcr_to_rdmar(rqst);
 	req->rl_reply = rep;
