[PATCH v2 11/20] xprtrdma: Prevent req creation while unloading the underlying device

[Chuck Lever <chuck.lever@xxxxxxxxxx>]

In a subsequent patch, we'll be invoking rpcrdma_req_create()
during transport operation. To protect the walk of rb_allreqs in
rpcrdma_ia_remove, block creation of rpcrdma_reqs while a removal
is in progress.

Because the caller of ->close is holding the transport send lock,
there can be only one call at a time. We don't need the test_and_set
mechanism to prevent multiple callers to rpcrdma_ia_remove.

Comments are clarified to note how the data structures are
protected.

Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
---
 net/sunrpc/xprtrdma/transport.c |    3 ++-
 net/sunrpc/xprtrdma/verbs.c     |   18 ++++++++++++++----
 2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/net/sunrpc/xprtrdma/transport.c b/net/sunrpc/xprtrdma/transport.c
index 2ba8be1..3cbc9b7 100644
--- a/net/sunrpc/xprtrdma/transport.c
+++ b/net/sunrpc/xprtrdma/transport.c
@@ -446,9 +446,10 @@
 
 	dprintk("RPC:       %s: closing xprt %p\n", __func__, xprt);
 
-	if (test_and_clear_bit(RPCRDMA_IAF_REMOVING, &ia->ri_flags)) {
+	if (test_bit(RPCRDMA_IAF_REMOVING, &ia->ri_flags)) {
 		xprt_clear_connected(xprt);
 		rpcrdma_ia_remove(ia);
+		clear_bit(RPCRDMA_IAF_REMOVING, &ia->ri_flags);
 		return;
 	}
 	if (ep->rep_connected == -ENODEV)
diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
index 42a6ef6..6308e60 100644
--- a/net/sunrpc/xprtrdma/verbs.c
+++ b/net/sunrpc/xprtrdma/verbs.c
@@ -452,8 +452,7 @@
  * rpcrdma_ia_remove - Handle device driver unload
  * @ia: interface adapter being removed
  *
- * Divest transport H/W resources associated with this adapter,
- * but allow it to be restored later.
+ * Caller holds the transport send lock.
  */
 void
 rpcrdma_ia_remove(struct rpcrdma_ia *ia)
@@ -484,16 +483,23 @@
 	ib_free_cq(ep->rep_attr.send_cq);
 	ep->rep_attr.send_cq = NULL;
 
-	/* The ULP is responsible for ensuring all DMA
-	 * mappings and MRs are gone.
+	/* The ib_drain_qp above guarantees that all posted
+	 * Receives have flushed, which returns the transport's
+	 * rpcrdma_reps to the rb_recv_bufs list.
 	 */
 	list_for_each_entry(rep, &buf->rb_recv_bufs, rr_list)
 		rpcrdma_dma_unmap_regbuf(rep->rr_rdmabuf);
+
+	/* DMA mapping happens in ->send_request with the
+	 * transport send lock held. Our caller is holding
+	 * the transport send lock.
+	 */
 	list_for_each_entry(req, &buf->rb_allreqs, rl_all) {
 		rpcrdma_dma_unmap_regbuf(req->rl_rdmabuf);
 		rpcrdma_dma_unmap_regbuf(req->rl_sendbuf);
 		rpcrdma_dma_unmap_regbuf(req->rl_recvbuf);
 	}
+
 	rpcrdma_mrs_destroy(buf);
 	ib_dealloc_pd(ia->ri_pd);
 	ia->ri_pd = NULL;
@@ -1071,9 +1077,13 @@ struct rpcrdma_sendctx *rpcrdma_sendctx_get_locked(struct rpcrdma_buffer *buf)
 struct rpcrdma_req *
 rpcrdma_req_create(struct rpcrdma_buffer *buffer, gfp_t flags)
 {
+	struct rpcrdma_ia *ia = rdmab_to_ia(buffer);
 	struct rpcrdma_regbuf *rb;
 	struct rpcrdma_req *req;
 
+	if (test_bit(RPCRDMA_IAF_REMOVING, &ia->ri_flags))
+		return NULL;
+
 	req = kzalloc(sizeof(*req), flags);
 	if (req == NULL)
 		return NULL;