net_sched: transform qdisc running bit into a seqcount

Instead of using a single bit (__QDISC___STATE_RUNNING)
in sch->__state, use a seqcount.

This adds lockdep support, but more importantly it will allow us
to sample qdisc/class statistics without having to grab qdisc root lock.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 11 deletions

diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index a1fd76c22a59..bff8d895ef8a 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -29,13 +29,6 @@ enum qdisc_state_t {
         __QDISC_STATE_THROTTLED,
 };
 
-/*
- * following bits are only changed while qdisc lock is held
- */
-enum qdisc___state_t {
-        __QDISC___STATE_RUNNING = 1,
-};
-
 struct qdisc_size_table {
         struct rcu_head         rcu;
         struct list_head        list;
@@ -93,7 +86,7 @@ struct Qdisc {
         unsigned long           state;
         struct sk_buff_head     q;
         struct gnet_stats_basic_packed bstats;
-        unsigned int            __state;
+        seqcount_t              running;
         struct gnet_stats_queue qstats;
         struct rcu_head         rcu_head;
         int                     padded;
@@ -104,20 +97,20 @@ struct Qdisc {
 
 static inline bool qdisc_is_running(const struct Qdisc *qdisc)
 {
-        return (qdisc->__state & __QDISC___STATE_RUNNING) ? true : false;
+        return (raw_read_seqcount(&qdisc->running) & 1) ? true : false;
 }
 
 static inline bool qdisc_run_begin(struct Qdisc *qdisc)
 {
         if (qdisc_is_running(qdisc))
                 return false;
-        qdisc->__state |= __QDISC___STATE_RUNNING;
+        write_seqcount_begin(&qdisc->running);
         return true;
 }
 
 static inline void qdisc_run_end(struct Qdisc *qdisc)
 {
-        qdisc->__state &= ~__QDISC___STATE_RUNNING;
+        write_seqcount_end(&qdisc->running);
 }
 
 static inline bool qdisc_may_bulk(const struct Qdisc *qdisc)