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>

3 files changed, 6 insertions, 8 deletions

diff --git a/include/linux/sunrpc/svc_rdma.h b/include/linux/sunrpc/svc_rdma.h
index ef2e3a20bf3b..dc05b54bd3a3 100644
--- a/include/linux/sunrpc/svc_rdma.h
+++ b/include/linux/sunrpc/svc_rdma.h
@@ -143,7 +143,6 @@ struct svcxprt_rdma {
         unsigned long        sc_flags;
         struct list_head     sc_dto_q;          /* DTO tasklet I/O pending Q */
         struct list_head     sc_read_complete_q;
-        spinlock_t           sc_read_complete_lock;
         struct work_struct   sc_work;
 };
 /* sc_flags */
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,
diff --git a/net/sunrpc/xprtrdma/svc_rdma_transport.c b/net/sunrpc/xprtrdma/svc_rdma_transport.c
index 19ddc382b777..900cb69728c6 100644
--- a/net/sunrpc/xprtrdma/svc_rdma_transport.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_transport.c
@@ -359,11 +359,11 @@ static void sq_cq_reap(struct svcxprt_rdma *xprt)
                         if (test_bit(RDMACTXT_F_LAST_CTXT, &ctxt->flags)) {
                                 struct svc_rdma_op_ctxt *read_hdr = ctxt->read_hdr;
                                 BUG_ON(!read_hdr);
+                                spin_lock_bh(&xprt->sc_rq_dto_lock);
                                 set_bit(XPT_DATA, &xprt->sc_xprt.xpt_flags);
-                                spin_lock_bh(&xprt->sc_read_complete_lock);
                                 list_add_tail(&read_hdr->dto_q,
                                               &xprt->sc_read_complete_q);
-                                spin_unlock_bh(&xprt->sc_read_complete_lock);
+                                spin_unlock_bh(&xprt->sc_rq_dto_lock);
                                 svc_xprt_enqueue(&xprt->sc_xprt);
                         }
                         svc_rdma_put_context(ctxt, 0);
@@ -428,7 +428,6 @@ static struct svcxprt_rdma *rdma_create_xprt(struct svc_serv *serv,
         init_waitqueue_head(&cma_xprt->sc_send_wait);
 
         spin_lock_init(&cma_xprt->sc_lock);
-        spin_lock_init(&cma_xprt->sc_read_complete_lock);
         spin_lock_init(&cma_xprt->sc_rq_dto_lock);
 
         cma_xprt->sc_ord = svcrdma_ord;