Author: royger
Date: Fri May 19 08:19:51 2017
New Revision: 318523
URL: https://svnweb.freebsd.org/changeset/base/318523

Log:
  xen/netfront: don't drop the ring RX lock with inconsistent ring state
  
  Make sure the RX ring lock is only released when the state of the ring is
  consistent, or else concurrent calls to xn_rxeof might get an inconsistent 
ring
  state and thus some packets might be processed twice.
  
  Note that this is not very common, and could only happen when an interrupt is
  delivered while in xn_ifinit.
  
  Reported by:  cperciva
  Tested by:    cperciva
  MFC after:    1 week
  Sponsored by: Citrix Systems R&D

Modified:
  head/sys/dev/xen/netfront/netfront.c

Modified: head/sys/dev/xen/netfront/netfront.c
==============================================================================
--- head/sys/dev/xen/netfront/netfront.c        Fri May 19 08:19:39 2017        
(r318522)
+++ head/sys/dev/xen/netfront/netfront.c        Fri May 19 08:19:51 2017        
(r318523)
@@ -1161,17 +1161,18 @@ xn_rxeof(struct netfront_rxq *rxq)
        struct mbufq mbufq_rxq, mbufq_errq;
        int err, work_to_do;
 
-       do {
-               XN_RX_LOCK_ASSERT(rxq);
-               if (!netfront_carrier_ok(np))
-                       return;
-
-               /* XXX: there should be some sane limit. */
-               mbufq_init(&mbufq_errq, INT_MAX);
-               mbufq_init(&mbufq_rxq, INT_MAX);
+       XN_RX_LOCK_ASSERT(rxq);
+
+       if (!netfront_carrier_ok(np))
+               return;
+
+       /* XXX: there should be some sane limit. */
+       mbufq_init(&mbufq_errq, INT_MAX);
+       mbufq_init(&mbufq_rxq, INT_MAX);
 
-               ifp = np->xn_ifp;
+       ifp = np->xn_ifp;
 
+       do {
                rp = rxq->ring.sring->rsp_prod;
                rmb();  /* Ensure we see queued responses up to 'rp'. */
 
@@ -1191,7 +1192,7 @@ xn_rxeof(struct netfront_rxq *rxq)
                        }
 
                        m->m_pkthdr.rcvif = ifp;
-                       if ( rx->flags & NETRXF_data_validated ) {
+                       if (rx->flags & NETRXF_data_validated) {
                                /*
                                 * According to mbuf(9) the correct way to tell
                                 * the stack that the checksum of an inbound
@@ -1214,50 +1215,45 @@ xn_rxeof(struct netfront_rxq *rxq)
                        }
 
                        (void )mbufq_enqueue(&mbufq_rxq, m);
-                       rxq->ring.rsp_cons = i;
                }
 
-               mbufq_drain(&mbufq_errq);
+               rxq->ring.rsp_cons = i;
 
-               /*
-                * Process all the mbufs after the remapping is complete.
-                * Break the mbuf chain first though.
-                */
-               while ((m = mbufq_dequeue(&mbufq_rxq)) != NULL) {
-                       if_inc_counter(ifp, IFCOUNTER_IPACKETS, 1);
+               xn_alloc_rx_buffers(rxq);
 
-                       /* XXX: Do we really need to drop the rx lock? */
-                       XN_RX_UNLOCK(rxq);
+               RING_FINAL_CHECK_FOR_RESPONSES(&rxq->ring, work_to_do);
+       } while (work_to_do);
+
+       XN_RX_UNLOCK(rxq);
+       mbufq_drain(&mbufq_errq);
+       /*
+        * Process all the mbufs after the remapping is complete.
+        * Break the mbuf chain first though.
+        */
+       while ((m = mbufq_dequeue(&mbufq_rxq)) != NULL) {
+               if_inc_counter(ifp, IFCOUNTER_IPACKETS, 1);
 #if (defined(INET) || defined(INET6))
-                       /* Use LRO if possible */
-                       if ((ifp->if_capenable & IFCAP_LRO) == 0 ||
-                           lro->lro_cnt == 0 || tcp_lro_rx(lro, m, 0)) {
-                               /*
-                                * If LRO fails, pass up to the stack
-                                * directly.
-                                */
-                               (*ifp->if_input)(ifp, m);
-                       }
-#else
+               /* Use LRO if possible */
+               if ((ifp->if_capenable & IFCAP_LRO) == 0 ||
+                   lro->lro_cnt == 0 || tcp_lro_rx(lro, m, 0)) {
+                       /*
+                        * If LRO fails, pass up to the stack
+                        * directly.
+                        */
                        (*ifp->if_input)(ifp, m);
-#endif
-
-                       XN_RX_LOCK(rxq);
                }
-
-               rxq->ring.rsp_cons = i;
+#else
+               (*ifp->if_input)(ifp, m);
+#endif
+       }
 
 #if (defined(INET) || defined(INET6))
-               /*
-                * Flush any outstanding LRO work
-                */
-               tcp_lro_flush_all(lro);
+       /*
+        * Flush any outstanding LRO work
+        */
+       tcp_lro_flush_all(lro);
 #endif
-
-               xn_alloc_rx_buffers(rxq);
-
-               RING_FINAL_CHECK_FOR_RESPONSES(&rxq->ring, work_to_do);
-       } while (work_to_do);
+       XN_RX_LOCK(rxq);
 }
 
 static void
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