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>

diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index 144f264..fceddf8 100644 (file)
--- 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,
 };

diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
index 6a0eaca..76e0d12 100644 (file)
--- 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;
        }

diff --git a/net/sched/cls_flower.c b/net/sched/cls_flower.c
index 0d125de..b0f42e6 100644 (file)
--- 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,

diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
index 66c6bce..a0e6fac 100644 (file)
--- 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;