[ovs-dev] [ovs flow free panic v2] datapath: Fix kernel panic on ovs_flow_free

[Andy Zhou]

Both mega flow mask's reference counter and per flow table mask list
should only be accessed when holding ovs_mutex() lock. However
this is not true with ovs_flow_table_flush(). The patch fixes this bug.

Signed-off-by: Andy Zhou <azhou at nicira.com>
---
   v1->v2: 
	Atomic ops can protect mask's reference counter, but not mask list.
	rework ovs_flow_table_flush() implementation instead. 
---
 datapath/flow_table.c |   61 ++++++++++++++++++++++++-------------------------
 1 file changed, 30 insertions(+), 31 deletions(-)

diff --git a/datapath/flow_table.c b/datapath/flow_table.c
index 4232b82..f26c43f 100644
--- a/datapath/flow_table.c
+++ b/datapath/flow_table.c
@@ -162,29 +162,26 @@ static void rcu_free_sw_flow_mask_cb(struct rcu_head *rcu)
 	kfree(mask);
 }
 
-static void flow_mask_del_ref(struct sw_flow_mask *mask, bool deferred)
-{
-	if (!mask)
-		return;
-
-	BUG_ON(!mask->ref_count);
-	mask->ref_count--;
-
-	if (!mask->ref_count) {
-		list_del_rcu(&mask->list);
-		if (deferred)
-			call_rcu(&mask->rcu, rcu_free_sw_flow_mask_cb);
-		else
-			kfree(mask);
-	}
-}
-
 void ovs_flow_free(struct sw_flow *flow, bool deferred)
 {
 	if (!flow)
 		return;
 
-	flow_mask_del_ref(flow->mask, deferred);
+	if (flow->mask) {
+		struct sw_flow_mask *mask = flow->mask;
+
+		BUG_ON(!mask->ref_count);
+		mask->ref_count--;
+
+		if (!mask->ref_count) {
+			ASSERT_OVSL();
+			list_del_rcu(&mask->list);
+			if (deferred)
+				call_rcu(&mask->rcu, rcu_free_sw_flow_mask_cb);
+			else
+				kfree(mask);
+		}
+	}
 
 	if (deferred)
 		call_rcu(&flow->rcu, rcu_free_flow_callback);
@@ -197,12 +194,12 @@ static void free_buckets(struct flex_array *buckets)
 	flex_array_free(buckets);
 }
 
-static void __table_instance_destroy(struct table_instance *ti)
+static void table_instance_free_flows(struct table_instance *ti, bool deferred)
 {
 	int i;
 
 	if (ti->keep_flows)
-		goto skip_flows;
+		return;
 
 	for (i = 0; i < ti->n_buckets; i++) {
 		struct sw_flow *flow;
@@ -211,12 +208,14 @@ static void __table_instance_destroy(struct table_instance *ti)
 		int ver = ti->node_ver;
 
 		hlist_for_each_entry_safe(flow, n, head, hash_node[ver]) {
-			hlist_del(&flow->hash_node[ver]);
-			ovs_flow_free(flow, false);
+			hlist_del_rcu(&flow->hash_node[ver]);
+			ovs_flow_free(flow, deferred);
 		}
 	}
+}
 
-skip_flows:
+static void __table_instance_destroy(struct table_instance *ti)
+{
 	free_buckets(ti->buckets);
 	kfree(ti);
 }
@@ -262,7 +261,8 @@ static void flow_tbl_destroy_rcu_cb(struct rcu_head *rcu)
 {
 	struct table_instance *ti = container_of(rcu, struct table_instance, rcu);
 
-	__table_instance_destroy(ti);
+	free_buckets(ti->buckets);
+	kfree(ti);
 }
 
 static void table_instance_destroy(struct table_instance *ti, bool deferred)
@@ -270,6 +270,8 @@ static void table_instance_destroy(struct table_instance *ti, bool deferred)
 	if (!ti)
 		return;
 
+	table_instance_free_flows(ti, deferred);
+
 	if (deferred)
 		call_rcu(&ti->rcu, flow_tbl_destroy_rcu_cb);
 	else
@@ -513,16 +515,11 @@ static struct sw_flow_mask *mask_alloc(void)
 
 	mask = kmalloc(sizeof(*mask), GFP_KERNEL);
 	if (mask)
-		mask->ref_count = 0;
+		mask->ref_count = 1;
 
 	return mask;
 }
 
-static void mask_add_ref(struct sw_flow_mask *mask)
-{
-	mask->ref_count++;
-}
-
 static bool mask_equal(const struct sw_flow_mask *a,
 		       const struct sw_flow_mask *b)
 {
@@ -563,9 +560,11 @@ static int flow_mask_insert(struct flow_table *tbl, struct sw_flow *flow,
 		mask->key = new->key;
 		mask->range = new->range;
 		list_add_rcu(&mask->list, &tbl->mask_list);
+	} else {
+		BUG_ON(!mask->ref_count);
+		mask->ref_count++;
 	}
 
-	mask_add_ref(mask);
 	flow->mask = mask;
 	return 0;
 }
-- 
1.7.9.5