[PATCH v1 2/8] xprtrdma: Do not post Receives after disconnect

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

Currently the Receive completion handler refreshes the Receive Queue
whenever a successful Receive completion occurs.

On disconnect, xprtrdma drains the Receive Queue. The first few
Receive completions after a disconnect are typically successful,
until the first flushed Receive.

This means the Receive completion handler continues to post more
Receive WRs after the drain sentinel has been posted. The late-
posted Receives flush after the drain sentinel has completed,
leading to a crash later in rpcrdma_xprt_disconnect().

To prevent this crash, xprtrdma has to ensure that the Receive
handler stops posting Receives before ib_drain_rq() posts its
drain sentinel.

This patch is probably not sufficient to fully close that window,
but does significantly reduce the opportunity for a crash to
occur without incurring undue performance overhead.

Cc: stable@vger.kernel.org # v5.7
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 net/sunrpc/xprtrdma/verbs.c |    7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
index ec912cf9c618..1d88685badbe 100644
--- a/net/sunrpc/xprtrdma/verbs.c
+++ b/net/sunrpc/xprtrdma/verbs.c
@@ -1371,8 +1371,10 @@ void rpcrdma_post_recvs(struct rpcrdma_xprt *r_xprt, bool temp)
 {
 	struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
 	struct rpcrdma_ep *ep = r_xprt->rx_ep;
+	struct ib_qp_init_attr init_attr;
 	struct ib_recv_wr *wr, *bad_wr;
 	struct rpcrdma_rep *rep;
+	struct ib_qp_attr attr;
 	int needed, count, rc;
 
 	rc = 0;
@@ -1385,6 +1387,11 @@ void rpcrdma_post_recvs(struct rpcrdma_xprt *r_xprt, bool temp)
 	if (!temp)
 		needed += RPCRDMA_MAX_RECV_BATCH;
 
+	if (ib_query_qp(ep->re_id->qp, &attr, IB_QP_STATE, &init_attr))
+		goto out;
+	if (attr.qp_state == IB_QPS_ERR)
+		goto out;
+
 	/* fast path: all needed reps can be found on the free list */
 	wr = NULL;
 	while (needed) {