[ovs-dev] [PATCH 1/2] ofproto-dpif-upcall: Get rid of udpif_synchronize().

[Ben Pfaff]

RCU provides the semantics we want from udpif_synchronize() and it
should be much more lightweight than killing and restarting all the
upcall threads.  It looks like udpif_synchronize() was written before
the OVS tree had RCU support, which is probably why we didn't use it
here from the beginning.  So we can just change udpif_synchronize()
to a single ovsrcu_synchronize() call.

However, udpif_synchronize() only has a single caller, which calls
ovsrcu_synchronize() anyway just beforehand, via xlate_txn_commit().
So we can get rid of udpif_synchronize() entirely, which this patch
does.

As a side effect, this eliminates one reason why terminating OVS cleanly
clears the datapath flow table.  An upcoming patch will eliminate
other reasons.

Signed-off-by: Ben Pfaff <blp at ovn.org>
---
 ofproto/ofproto-dpif-upcall.c | 17 -----------------
 ofproto/ofproto-dpif-upcall.h |  1 -
 ofproto/ofproto-dpif-xlate.c  | 14 +++++++++-----
 ofproto/ofproto-dpif.c        |  4 ----
 4 files changed, 9 insertions(+), 27 deletions(-)

diff --git a/ofproto/ofproto-dpif-upcall.c b/ofproto/ofproto-dpif-upcall.c
index 657aa7f79208..9b3b4470b0af 100644
--- a/ofproto/ofproto-dpif-upcall.c
+++ b/ofproto/ofproto-dpif-upcall.c
@@ -643,23 +643,6 @@ udpif_set_threads(struct udpif *udpif, size_t n_handlers_,
     }
 }
 
-/* Waits for all ongoing upcall translations to complete.  This ensures that
- * there are no transient references to any removed ofprotos (or other
- * objects).  In particular, this should be called after an ofproto is removed
- * (e.g. via xlate_remove_ofproto()) but before it is destroyed. */
-void
-udpif_synchronize(struct udpif *udpif)
-{
-    /* This is stronger than necessary.  It would be sufficient to ensure
-     * (somehow) that each handler and revalidator thread had passed through
-     * its main loop once. */
-    size_t n_handlers_ = udpif->n_handlers;
-    size_t n_revalidators_ = udpif->n_revalidators;
-
-    udpif_stop_threads(udpif);
-    udpif_start_threads(udpif, n_handlers_, n_revalidators_);
-}
-
 /* Notifies 'udpif' that something changed which may render previous
  * xlate_actions() results invalid. */
 void
diff --git a/ofproto/ofproto-dpif-upcall.h b/ofproto/ofproto-dpif-upcall.h
index cef1d34198d6..693107ae56c1 100644
--- a/ofproto/ofproto-dpif-upcall.h
+++ b/ofproto/ofproto-dpif-upcall.h
@@ -33,7 +33,6 @@ struct udpif *udpif_create(struct dpif_backer *, struct dpif *);
 void udpif_run(struct udpif *udpif);
 void udpif_set_threads(struct udpif *, size_t n_handlers,
                        size_t n_revalidators);
-void udpif_synchronize(struct udpif *);
 void udpif_destroy(struct udpif *);
 void udpif_revalidate(struct udpif *);
 void udpif_get_memory_usage(struct udpif *, struct simap *usage);
diff --git a/ofproto/ofproto-dpif-xlate.c b/ofproto/ofproto-dpif-xlate.c
index f92cb62c80ce..e375dc1b085f 100644
--- a/ofproto/ofproto-dpif-xlate.c
+++ b/ofproto/ofproto-dpif-xlate.c
@@ -1165,11 +1165,15 @@ xlate_xport_copy(struct xbridge *xbridge, struct xbundle *xbundle,
  *
  * A sample workflow:
  *
- * xlate_txn_start();
- * ...
- * edit_xlate_configuration();
- * ...
- * xlate_txn_commit(); */
+ *     xlate_txn_start();
+ *     ...
+ *     edit_xlate_configuration();
+ *     ...
+ *     xlate_txn_commit();
+ *
+ * The ovsrcu_synchronize() call here also ensures that the upcall threads
+ * retain no references to anything in the previous configuration.
+ */
 void
 xlate_txn_commit(void)
 {
diff --git a/ofproto/ofproto-dpif.c b/ofproto/ofproto-dpif.c
index c35ec3e61592..d56629b005ea 100644
--- a/ofproto/ofproto-dpif.c
+++ b/ofproto/ofproto-dpif.c
@@ -1706,10 +1706,6 @@ destruct(struct ofproto *ofproto_, bool del)
     xlate_remove_ofproto(ofproto);
     xlate_txn_commit();
 
-    /* Ensure that the upcall processing threads have no remaining references
-     * to the ofproto or anything in it. */
-    udpif_synchronize(ofproto->backer->udpif);
-
     hmap_remove(&all_ofproto_dpifs_by_name,
                 &ofproto->all_ofproto_dpifs_by_name_node);
     hmap_remove(&all_ofproto_dpifs_by_uuid,
-- 
2.21.0