linux-kernel - [PATCH 5.6 122/167] SUNRPC: Fix backchannel RPC soft lockups

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Date:   Tue, 28 Apr 2020 20:24:58 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Trond Myklebust <trondmy@...merspace.com>,
        Chuck Lever <chuck.lever@...cle.com>
Subject: [PATCH 5.6 122/167] SUNRPC: Fix backchannel RPC soft lockups

From: Chuck Lever <chuck.lever@...cle.com>

commit 6221f1d9b63fed6260273e59a2b89ab30537a811 upstream.

Currently, after the forward channel connection goes away,
backchannel operations are causing soft lockups on the server
because call_transmit_status's SOFTCONN logic ignores ENOTCONN.
Such backchannel Calls are aggressively retried until the client
reconnects.

Backchannel Calls should use RPC_TASK_NOCONNECT rather than
RPC_TASK_SOFTCONN. If there is no forward connection, the server is
not capable of establishing a connection back to the client, thus
that backchannel request should fail before the server attempts to
send it. Commit 58255a4e3ce5 ("NFSD: NFSv4 callback client should
use RPC_TASK_SOFTCONN") was merged several years before
RPC_TASK_NOCONNECT was available.

Because setup_callback_client() explicitly sets NOPING, the NFSv4.0
callback connection depends on the first callback RPC to initiate
a connection to the client. Thus NFSv4.0 needs to continue to use
RPC_TASK_SOFTCONN.

Suggested-by: Trond Myklebust <trondmy@...merspace.com>
Signed-off-by: Chuck Lever <chuck.lever@...cle.com>
Cc: <stable@...r.kernel.org> # v4.20+
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/nfsd/nfs4callback.c                     |    4 +++-
 net/sunrpc/svc_xprt.c                      |    2 ++
 net/sunrpc/xprtrdma/svc_rdma_backchannel.c |    2 ++
 net/sunrpc/xprtsock.c                      |    1 +
 4 files changed, 8 insertions(+), 1 deletion(-)

--- a/fs/nfsd/nfs4callback.c
+++ b/fs/nfsd/nfs4callback.c
@@ -1312,6 +1312,7 @@ nfsd4_run_cb_work(struct work_struct *wo
 		container_of(work, struct nfsd4_callback, cb_work);
 	struct nfs4_client *clp = cb->cb_clp;
 	struct rpc_clnt *clnt;
+	int flags;
 
 	if (cb->cb_need_restart) {
 		cb->cb_need_restart = false;
@@ -1340,7 +1341,8 @@ nfsd4_run_cb_work(struct work_struct *wo
 	}
 
 	cb->cb_msg.rpc_cred = clp->cl_cb_cred;
-	rpc_call_async(clnt, &cb->cb_msg, RPC_TASK_SOFT | RPC_TASK_SOFTCONN,
+	flags = clp->cl_minorversion ? RPC_TASK_NOCONNECT : RPC_TASK_SOFTCONN;
+	rpc_call_async(clnt, &cb->cb_msg, RPC_TASK_SOFT | flags,
 			cb->cb_ops ? &nfsd4_cb_ops : &nfsd4_cb_probe_ops, cb);
 }
 
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -1028,6 +1028,8 @@ static void svc_delete_xprt(struct svc_x
 
 	dprintk("svc: svc_delete_xprt(%p)\n", xprt);
 	xprt->xpt_ops->xpo_detach(xprt);
+	if (xprt->xpt_bc_xprt)
+		xprt->xpt_bc_xprt->ops->close(xprt->xpt_bc_xprt);
 
 	spin_lock_bh(&serv->sv_lock);
 	list_del_init(&xprt->xpt_list);
--- a/net/sunrpc/xprtrdma/svc_rdma_backchannel.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_backchannel.c
@@ -242,6 +242,8 @@ static void
 xprt_rdma_bc_close(struct rpc_xprt *xprt)
 {
 	dprintk("svcrdma: %s: xprt %p\n", __func__, xprt);
+
+	xprt_disconnect_done(xprt);
 	xprt->cwnd = RPC_CWNDSHIFT;
 }
 
--- a/net/sunrpc/xprtsock.c
+++ b/net/sunrpc/xprtsock.c
@@ -2714,6 +2714,7 @@ static int bc_send_request(struct rpc_rq
 
 static void bc_close(struct rpc_xprt *xprt)
 {
+	xprt_disconnect_done(xprt);
 }
 
 /*