svcrdma: Fix race between svc_rdma_recvfrom thread and the dto_tasklet

RDMA_READ completions are kept on a separate queue from the general
I/O request queue. Since a separate lock is used to protect the RDMA_READ
completion queue, a race exists between the dto_tasklet and the
svc_rdma_recvfrom thread where the dto_tasklet sets the XPT_DATA
bit and adds I/O to the read-completion queue. Concurrently, the
recvfrom thread checks the generic queue, finds it empty and resets
the XPT_DATA bit. A subsequent svc_xprt_enqueue will fail to enqueue
the transport for I/O and cause the transport to "stall".

The fix is to protect both lists with the same lock and set the XPT_DATA
bit with this lock held.

Signed-off-by: Tom Tucker <tom@opengridcomputing.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

1 files changed, 4 insertions, 4 deletions

diff --git a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
index b4b17f44cb29..74de31a06616 100644
--- a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
@@ -443,18 +443,18 @@ int svc_rdma_recvfrom(struct svc_rqst *rqstp)
 
         dprintk("svcrdma: rqstp=%p\n", rqstp);
 
-        spin_lock_bh(&rdma_xprt->sc_read_complete_lock);
+        spin_lock_bh(&rdma_xprt->sc_rq_dto_lock);
         if (!list_empty(&rdma_xprt->sc_read_complete_q)) {
                 ctxt = list_entry(rdma_xprt->sc_read_complete_q.next,
                                   struct svc_rdma_op_ctxt,
                                   dto_q);
                 list_del_init(&ctxt->dto_q);
         }
-        spin_unlock_bh(&rdma_xprt->sc_read_complete_lock);
-        if (ctxt)
+        if (ctxt) {
+                spin_unlock_bh(&rdma_xprt->sc_rq_dto_lock);
                 return rdma_read_complete(rqstp, ctxt);
+        }
 
-        spin_lock_bh(&rdma_xprt->sc_rq_dto_lock);
         if (!list_empty(&rdma_xprt->sc_rq_dto_q)) {
                 ctxt = list_entry(rdma_xprt->sc_rq_dto_q.next,
                                   struct svc_rdma_op_ctxt,