net/sched: add delete_empty() to filters and use it in cls_flower

Revert "net/sched: cls_u32: fix refcount leak in the error path of
u32_change()", and fix the u32 refcount leak in a more generic way that
preserves the semantic of rule dumping.
On tc filters that don't support lockless insertion/removal, there is no
need to guard against concurrent insertion when a removal is in progress.
Therefore, for most of them we can avoid a full walk() when deleting, and
just decrease the refcount, like it was done on older Linux kernels.
This fixes situations where walk() was wrongly detecting a non-empty
filter, like it happened with cls_u32 in the error path of change(), thus
leading to failures in the following tdc selftests:

 6aa7: (filter, u32) Add/Replace u32 with source match and invalid indev
 6658: (filter, u32) Add/Replace u32 with custom hash table and invalid handle
 74c2: (filter, u32) Add/Replace u32 filter with invalid hash table id

On cls_flower, and on (future) lockless filters, this check is necessary:
move all the check_empty() logic in a callback so that each filter
can have its own implementation. For cls_flower, it's sufficient to check
if no IDRs have been allocated.

This reverts commit 275c44aa194b7159d1191817b20e076f55f0e620.

Changes since v1:
 - document the need for delete_empty() when TCF_PROTO_OPS_DOIT_UNLOCKED
   is used, thanks to Vlad Buslov
 - implement delete_empty() without doing fl_walk(), thanks to Vlad Buslov
 - squash revert and new fix in a single patch, to be nice with bisect
   tests that run tdc on u32 filter, thanks to Dave Miller

Fixes: 275c44aa194b ("net/sched: cls_u32: fix refcount leak in the error path of u32_change()")
Fixes: 6676d5e416ee ("net: sched: set dedicated tcf_walker flag when tp is empty")
Suggested-by: Jamal Hadi Salim <jhs@mojatatu.com>
Suggested-by: Vlad Buslov <vladbu@mellanox.com>
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Reviewed-by: Vlad Buslov <vladbu@mellanox.com>
Tested-by: Jamal Hadi Salim <jhs@mojatatu.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 26 deletions

diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
index 6a0eacafdb19..76e0d122616a 100644
--- a/net/sched/cls_api.c
+++ b/net/sched/cls_api.c
@@ -308,33 +308,12 @@ static void tcf_proto_put(struct tcf_proto *tp, bool rtnl_held,
 		tcf_proto_destroy(tp, rtnl_held, true, extack);
 }
 
-static int walker_check_empty(struct tcf_proto *tp, void *fh,
-			      struct tcf_walker *arg)
+static bool tcf_proto_check_delete(struct tcf_proto *tp)
 {
-	if (fh) {
-		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_check_empty, };
-
-	if (tp->ops->walk) {
-		tp->ops->walk(tp, &walker, rtnl_held);
-		return !walker.nonempty;
-	}
-	return true;
-}
+	if (tp->ops->delete_empty)
+		return tp->ops->delete_empty(tp);
 
-static bool tcf_proto_check_delete(struct tcf_proto *tp, bool rtnl_held)
-{
-	spin_lock(&tp->lock);
-	if (tcf_proto_is_empty(tp, rtnl_held))
-		tp->deleting = true;
-	spin_unlock(&tp->lock);
+	tp->deleting = true;
 	return tp->deleting;
 }
 
@@ -1751,7 +1730,7 @@ static void tcf_chain_tp_delete_empty(struct tcf_chain *chain,
 	 * concurrently.
 	 * Mark tp for deletion if it is empty.
 	 */
-	if (!tp_iter || !tcf_proto_check_delete(tp, rtnl_held)) {
+	if (!tp_iter || !tcf_proto_check_delete(tp)) {
 		mutex_unlock(&chain->filter_chain_lock);
 		return;
 	}