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, 12 insertions, 0 deletions

diff --git a/net/sched/cls_flower.c b/net/sched/cls_flower.c
index 0d125de54285..b0f42e62dd76 100644
--- a/net/sched/cls_flower.c
+++ b/net/sched/cls_flower.c
@@ -2773,6 +2773,17 @@ static void fl_bind_class(void *fh, u32 classid, unsigned long cl)
 		f->res.class = cl;
 }
 
+static bool fl_delete_empty(struct tcf_proto *tp)
+{
+	struct cls_fl_head *head = fl_head_dereference(tp);
+
+	spin_lock(&tp->lock);
+	tp->deleting = idr_is_empty(&head->handle_idr);
+	spin_unlock(&tp->lock);
+
+	return tp->deleting;
+}
+
 static struct tcf_proto_ops cls_fl_ops __read_mostly = {
 	.kind		= "flower",
 	.classify	= fl_classify,
@@ -2782,6 +2793,7 @@ static struct tcf_proto_ops cls_fl_ops __read_mostly = {
 	.put		= fl_put,
 	.change		= fl_change,
 	.delete		= fl_delete,
+	.delete_empty	= fl_delete_empty,
 	.walk		= fl_walk,
 	.reoffload	= fl_reoffload,
 	.hw_add		= fl_hw_add,