[PATCH 5.4 152/191] net/sched: add delete_empty() to filters and use it in cls_flower

Greg Kroah-Hartman
2020-01-02T22:17:00Z

From: Davide Caratti <dcaratti@redhat.com>

[ Upstream commit a5b72a083da197b493c7ed1e5730d62d3199f7d6 ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/net/sch_generic.h | 5 +++++
net/sched/cls_api.c | 31 +++++--------------------------
net/sched/cls_flower.c | 12 ++++++++++++
3 files changed, 22 insertions(+), 26 deletions(-)

--- 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,
};
--- a/net/sched/cls_api.c
+++ b/net/sched/cls_api.c
@@ -308,33 +308,12 @@ static void tcf_proto_put(struct tcf_pro
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(st
* 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;
}
--- a/net/sched/cls_flower.c
+++ b/net/sched/cls_flower.c
@@ -2519,6 +2519,17 @@ static void fl_bind_class(void *fh, u32
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,
@@ -2528,6 +2539,7 @@ static struct tcf_proto_ops cls_fl_ops _
.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,