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[NET_SCHED]: Fix fallout from dev->qdisc RCU change

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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>
This commit is contained in:
Patrick McHardy
2006-09-27 16:45:45 -07:00
committed by David S. Miller
parent 787e0617e5
commit 85670cc1fa
4 changed files with 39 additions and 61 deletions
Download Patch File Download Diff File Expand all files Collapse all files

66
net/sched/sch_generic.c
View File

@@ -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 @@ DEFINE_RWLOCK(qdisc_tree_lock);
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 @@ void qdisc_reset(struct Qdisc *qdisc)
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 @@ static void __qdisc_destroy(struct rcu_head *head)
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);
}
/* 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);
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);
module_put(ops->owner);
dev_put(qdisc->dev);
call_rcu(&qdisc->q_rcu, __qdisc_destroy);
}
@@ -549,15 +525,15 @@ void dev_activate(struct net_device *dev)
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))