[PATCH v3 net-next 1/5] net: sched: fix qdisc->running lockdep annotations

[Eric Dumazet]

1) qdisc_run_begin() is really using the equivalent of a trylock.
  Instead of using write_seqcount_begin(), use a combination of
  raw_write_seqcount_begin() and correct lockdep annotation.

2) sch_direct_xmit() should use regular spin_lock(root_lock)

Fixes: f9eb8aea2a1e ("net_sched: transform qdisc running bit into a seqcount")
Signed-off-by: Eric Dumazet <eduma...@google.com>
Reported-by: David Ahern <d...@cumulusnetworks.com>
---
 include/net/sch_generic.h | 6 +++++-
 net/sched/sch_generic.c   | 4 ++--
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index c4f5749342ec..d53ecfc1d60e 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -104,7 +104,11 @@ static inline bool qdisc_run_begin(struct Qdisc *qdisc)
 {
        if (qdisc_is_running(qdisc))
                return false;
-       write_seqcount_begin(&qdisc->running);
+       /* Variant of write_seqcount_begin() telling lockdep a trylock
+        * was attempted.
+        */
+       raw_write_seqcount_begin(&qdisc->running);
+       seqcount_acquire(&qdisc->running.dep_map, 0, 1, _RET_IP_);
        return true;
 }
 
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index cebea73e70ac..cad810b45e31 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -137,10 +137,10 @@ int sch_direct_xmit(struct sk_buff *skb, struct Qdisc *q,
 
                HARD_TX_UNLOCK(dev, txq);
        } else {
-               spin_lock_nested(root_lock, SINGLE_DEPTH_NESTING);
+               spin_lock(root_lock);
                return qdisc_qlen(q);
        }
-       spin_lock_nested(root_lock, SINGLE_DEPTH_NESTING);
+       spin_lock(root_lock);
 
        if (dev_xmit_complete(ret)) {
                /* Driver sent out skb successfully or skb was consumed */
-- 
2.8.0.rc3.226.g39d4020