[NET_SCHED]: Fix fallout from dev->qdisc RCU change
The move of qdisc destruction to a rcu callback broke locking in the
entire qdisc layer by invalidating previously valid assumptions about
the context in which changes to the qdisc tree occur.
The two assumptions were:
- since changes only happen in process context, read_lock doesn't need
bottem half protection. Now invalid since destruction of inner qdiscs,
classifiers, actions and estimators happens in the RCU callback unless
they're manually deleted, resulting in dead-locks when read_lock in
process context is interrupted by write_lock_bh in bottem half context.
- since changes only happen under the RTNL, no additional locking is
necessary for data not used during packet processing (f.e. u32_list).
Again, since destruction now happens in the RCU callback, this assumption
is not valid anymore, causing races while using this data, which can
result in corruption or use-after-free.
Instead of "fixing" this by disabling bottem halfs everywhere and adding
new locks/refcounting, this patch makes these assumptions valid again by
moving destruction back to process context. Since only the dev->qdisc
pointer is protected by RCU, but ->enqueue and the qdisc tree are still
protected by dev->qdisc_lock, destruction of the tree can be performed
immediately and only the final free needs to happen in the rcu callback
to make sure dev_queue_xmit doesn't access already freed memory.
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
index 7e14f14..37a1840 100644
--- a/net/sched/cls_api.c
+++ b/net/sched/cls_api.c
@@ -401,7 +401,7 @@
if ((dev = dev_get_by_index(tcm->tcm_ifindex)) == NULL)
return skb->len;
- read_lock_bh(&qdisc_tree_lock);
+ read_lock(&qdisc_tree_lock);
if (!tcm->tcm_parent)
q = dev->qdisc_sleeping;
else
@@ -458,7 +458,7 @@
if (cl)
cops->put(q, cl);
out:
- read_unlock_bh(&qdisc_tree_lock);
+ read_unlock(&qdisc_tree_lock);
dev_put(dev);
return skb->len;
}