xprtrdma: Add ro_unmap_safe memreg method

There needs to be a safe method of releasing registered memory
resources when an RPC terminates. Safe can mean a number of things:

+ Doesn't have to sleep

+ Doesn't rely on having a QP in RTS

ro_unmap_safe will be that safe method. It can be used in cases
where synchronous memory invalidation can deadlock, or needs to have
an active QP.

The important case is fencing an RPC's memory regions after it is
signaled (^C) and before it exits. If this is not done, there is a
window where the server can write an RPC reply into memory that the
client has released and re-used for some other purpose.

Note that this is a full solution for FRWR, but FMR and physical
still have some gaps where a particularly bad server can wreak
some havoc on the client. These gaps are not made worse by this
patch and are expected to be exceptionally rare and timing-based.
They are noted in documenting comments.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

1 files changed, 3 insertions, 6 deletions

diff --git a/net/sunrpc/xprtrdma/transport.c b/net/sunrpc/xprtrdma/transport.c
index 16595ff91994..99d2e5b72726 100644
--- a/net/sunrpc/xprtrdma/transport.c
+++ b/net/sunrpc/xprtrdma/transport.c
@@ -514,6 +514,7 @@ xprt_rdma_allocate(struct rpc_task *task, size_t size)
 out:
 	dprintk("RPC:       %s: size %zd, request 0x%p\n", __func__, size, req);
 	req->rl_connect_cookie = 0;	/* our reserved value */
+	req->rl_task = task;
 	return req->rl_sendbuf->rg_base;
 
 out_rdmabuf:
@@ -570,7 +571,6 @@ xprt_rdma_free(void *buffer)
 	struct rpcrdma_req *req;
 	struct rpcrdma_xprt *r_xprt;
 	struct rpcrdma_regbuf *rb;
-	int i;
 
 	if (buffer == NULL)
 		return;
@@ -584,11 +584,8 @@ xprt_rdma_free(void *buffer)
 
 	dprintk("RPC:       %s: called on 0x%p\n", __func__, req->rl_reply);
 
-	for (i = 0; req->rl_nchunks;) {
-		--req->rl_nchunks;
-		i += r_xprt->rx_ia.ri_ops->ro_unmap(r_xprt,
-						    &req->rl_segments[i]);
-	}
+	r_xprt->rx_ia.ri_ops->ro_unmap_safe(r_xprt, req,
+					    !RPC_IS_ASYNC(req->rl_task));
 
 	rpcrdma_buffer_put(req);
 }