[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/sch_generic.c b/net/sched/sch_generic.c
index 6f91518..88c6a99 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -45,11 +45,10 @@
The idea is the following:
- enqueue, dequeue are serialized via top level device
spinlock dev->queue_lock.
- - tree walking is protected by read_lock_bh(qdisc_tree_lock)
+ - tree walking is protected by read_lock(qdisc_tree_lock)
and this lock is used only in process context.
- - updates to tree are made under rtnl semaphore or
- from softirq context (__qdisc_destroy rcu-callback)
- hence this lock needs local bh disabling.
+ - updates to tree are made only under rtnl semaphore,
+ hence this lock may be made without local bh disabling.
qdisc_tree_lock must be grabbed BEFORE dev->queue_lock!
*/
@@ -57,14 +56,14 @@
void qdisc_lock_tree(struct net_device *dev)
{
- write_lock_bh(&qdisc_tree_lock);
+ write_lock(&qdisc_tree_lock);
spin_lock_bh(&dev->queue_lock);
}
void qdisc_unlock_tree(struct net_device *dev)
{
spin_unlock_bh(&dev->queue_lock);
- write_unlock_bh(&qdisc_tree_lock);
+ write_unlock(&qdisc_tree_lock);
}
/*
@@ -483,20 +482,6 @@
static void __qdisc_destroy(struct rcu_head *head)
{
struct Qdisc *qdisc = container_of(head, struct Qdisc, q_rcu);
- struct Qdisc_ops *ops = qdisc->ops;
-
-#ifdef CONFIG_NET_ESTIMATOR
- gen_kill_estimator(&qdisc->bstats, &qdisc->rate_est);
-#endif
- write_lock(&qdisc_tree_lock);
- if (ops->reset)
- ops->reset(qdisc);
- if (ops->destroy)
- ops->destroy(qdisc);
- write_unlock(&qdisc_tree_lock);
- module_put(ops->owner);
-
- dev_put(qdisc->dev);
kfree((char *) qdisc - qdisc->padded);
}
@@ -504,32 +489,23 @@
void qdisc_destroy(struct Qdisc *qdisc)
{
- struct list_head cql = LIST_HEAD_INIT(cql);
- struct Qdisc *cq, *q, *n;
+ struct Qdisc_ops *ops = qdisc->ops;
if (qdisc->flags & TCQ_F_BUILTIN ||
- !atomic_dec_and_test(&qdisc->refcnt))
+ !atomic_dec_and_test(&qdisc->refcnt))
return;
- if (!list_empty(&qdisc->list)) {
- if (qdisc->ops->cl_ops == NULL)
- list_del(&qdisc->list);
- else
- list_move(&qdisc->list, &cql);
- }
+ list_del(&qdisc->list);
+#ifdef CONFIG_NET_ESTIMATOR
+ gen_kill_estimator(&qdisc->bstats, &qdisc->rate_est);
+#endif
+ if (ops->reset)
+ ops->reset(qdisc);
+ if (ops->destroy)
+ ops->destroy(qdisc);
- /* unlink inner qdiscs from dev->qdisc_list immediately */
- list_for_each_entry(cq, &cql, list)
- list_for_each_entry_safe(q, n, &qdisc->dev->qdisc_list, list)
- if (TC_H_MAJ(q->parent) == TC_H_MAJ(cq->handle)) {
- if (q->ops->cl_ops == NULL)
- list_del_init(&q->list);
- else
- list_move_tail(&q->list, &cql);
- }
- list_for_each_entry_safe(cq, n, &cql, list)
- list_del_init(&cq->list);
-
+ module_put(ops->owner);
+ dev_put(qdisc->dev);
call_rcu(&qdisc->q_rcu, __qdisc_destroy);
}
@@ -549,15 +525,15 @@
printk(KERN_INFO "%s: activation failed\n", dev->name);
return;
}
- write_lock_bh(&qdisc_tree_lock);
+ write_lock(&qdisc_tree_lock);
list_add_tail(&qdisc->list, &dev->qdisc_list);
- write_unlock_bh(&qdisc_tree_lock);
+ write_unlock(&qdisc_tree_lock);
} else {
qdisc = &noqueue_qdisc;
}
- write_lock_bh(&qdisc_tree_lock);
+ write_lock(&qdisc_tree_lock);
dev->qdisc_sleeping = qdisc;
- write_unlock_bh(&qdisc_tree_lock);
+ write_unlock(&qdisc_tree_lock);
}
if (!netif_carrier_ok(dev))