[PATCH net-next] net: sched: set dedicated tcf_walker flag when tp is empty

[Vlad Buslov]

Using tcf_walker->stop flag to determine when tcf_walker->fn() was called
at least once is unreliable. Some classifiers set 'stop' flag on error
before calling walker callback, other classifiers used to call it with NULL
filter pointer when empty. In order to prevent further regressions, extend
tcf_walker structure with dedicated 'nonempty' flag. Set this flag in
tcf_walker->fn() implementation that is used to check if classifier has
filters configured.

Fixes: 8b64678e0af8 ("net: sched: refactor tp insert/delete for concurrent 
execution")
Signed-off-by: Vlad Buslov <vla...@mellanox.com>
Suggested-by: Cong Wang <xiyou.wangc...@gmail.com>
---
 include/net/pkt_cls.h |  1 +
 net/sched/cls_api.c   | 13 +++++++++----
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/include/net/pkt_cls.h b/include/net/pkt_cls.h
index 232f801f2a21..422dd8800478 100644
--- a/include/net/pkt_cls.h
+++ b/include/net/pkt_cls.h
@@ -17,6 +17,7 @@ struct tcf_walker {
        int     stop;
        int     skip;
        int     count;
+       bool    nonempty;
        unsigned long cookie;
        int     (*fn)(struct tcf_proto *, void *node, struct tcf_walker *);
 };
diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
index e2c888961379..3543be31d400 100644
--- a/net/sched/cls_api.c
+++ b/net/sched/cls_api.c
@@ -238,18 +238,23 @@ static void tcf_proto_put(struct tcf_proto *tp, bool 
rtnl_held,
                tcf_proto_destroy(tp, rtnl_held, extack);
 }
 
-static int walker_noop(struct tcf_proto *tp, void *d, struct tcf_walker *arg)
+static int walker_check_empty(struct tcf_proto *tp, void *d,
+                             struct tcf_walker *arg)
 {
-       return -1;
+       if (tp) {
+               arg->nonempty = true;
+               return -1;
+       }
+       return 0;
 }
 
 static bool tcf_proto_is_empty(struct tcf_proto *tp, bool rtnl_held)
 {
-       struct tcf_walker walker = { .fn = walker_noop, };
+       struct tcf_walker walker = { .fn = walker_check_empty, };
 
        if (tp->ops->walk) {
                tp->ops->walk(tp, &walker, rtnl_held);
-               return !walker.stop;
+               return !walker.nonempty;
        }
        return true;
 }
-- 
2.13.6