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, 0 deletions

diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index 144f264ea394..fceddf89592a 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -308,6 +308,7 @@ struct tcf_proto_ops {
 	int			(*delete)(struct tcf_proto *tp, void *arg,
 					  bool *last, bool rtnl_held,
 					  struct netlink_ext_ack *);
+	bool			(*delete_empty)(struct tcf_proto *tp);
 	void			(*walk)(struct tcf_proto *tp,
 					struct tcf_walker *arg, bool rtnl_held);
 	int			(*reoffload)(struct tcf_proto *tp, bool add,
@@ -336,6 +337,10 @@ struct tcf_proto_ops {
 	int			flags;
 };
 
+/* Classifiers setting TCF_PROTO_OPS_DOIT_UNLOCKED in tcf_proto_ops->flags
+ * are expected to implement tcf_proto_ops->delete_empty(), otherwise race
+ * conditions can occur when filters are inserted/deleted simultaneously.
+ */
 enum tcf_proto_ops_flags {
 	TCF_PROTO_OPS_DOIT_UNLOCKED = 1,
 };