net: sched: protect block offload-related fields with rw_semaphore

In order to remove dependency on rtnl lock, extend tcf_block with 'cb_lock'
rwsem and use it to protect flow_block->cb_list and related counters from
concurrent modification. The lock is taken in read mode for read-only
traversal of cb_list in tc_setup_cb_call() and write mode in all other
cases. This approach ensures that:

- cb_list is not changed concurrently while filters is being offloaded on
  block.

- block->nooffloaddevcnt is checked while holding the lock in read mode,
  but is only changed by bind/unbind code when holding the cb_lock in write
  mode to prevent concurrent modification.

Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index d9f359af0b93..a3eaf5f9d28f 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -13,6 +13,7 @@
 #include <linux/refcount.h>
 #include <linux/workqueue.h>
 #include <linux/mutex.h>
+#include <linux/rwsem.h>
 #include <net/gen_stats.h>
 #include <net/rtnetlink.h>
 #include <net/flow_offload.h>
@@ -396,6 +397,7 @@ struct tcf_block {
 	refcount_t refcnt;
 	struct net *net;
 	struct Qdisc *q;
+	struct rw_semaphore cb_lock; /* protects cb_list and offload counters */
 	struct flow_block flow_block;
 	struct list_head owner_list;
 	bool keep_dst;