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, 0 insertions, 25 deletions

diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
index 66c6bcec16cb..a0e6fac613de 100644
--- a/net/sched/cls_u32.c
+++ b/net/sched/cls_u32.c
@@ -1108,33 +1108,10 @@ erridr:
 	return err;
 }
 
-static bool u32_hnode_empty(struct tc_u_hnode *ht, bool *non_root_ht)
-{
-	int i;
-
-	if (!ht)
-		return true;
-	if (!ht->is_root) {
-		*non_root_ht = true;
-		return false;
-	}
-	if (*non_root_ht)
-		return false;
-	if (ht->refcnt < 2)
-		return true;
-
-	for (i = 0; i <= ht->divisor; i++) {
-		if (rtnl_dereference(ht->ht[i]))
-			return false;
-	}
-	return true;
-}
-
 static void u32_walk(struct tcf_proto *tp, struct tcf_walker *arg,
 		     bool rtnl_held)
 {
 	struct tc_u_common *tp_c = tp->data;
-	bool non_root_ht = false;
 	struct tc_u_hnode *ht;
 	struct tc_u_knode *n;
 	unsigned int h;
@@ -1147,8 +1124,6 @@ static void u32_walk(struct tcf_proto *tp, struct tcf_walker *arg,
 	     ht = rtnl_dereference(ht->next)) {
 		if (ht->prio != tp->prio)
 			continue;
-		if (u32_hnode_empty(ht, &non_root_ht))
-			return;
 		if (arg->count >= arg->skip) {
 			if (arg->fn(tp, ht, arg) < 0) {
 				arg->stop = 1;