From 85670cc1faa2e1472e4a423cbf0b5e3d55c5ba88 Mon Sep 17 00:00:00 2001 From: Patrick McHardy Date: Wed, 27 Sep 2006 16:45:45 -0700 Subject: [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 Signed-off-by: David S. Miller --- net/sched/sch_generic.c | 66 ++++++++++++++++--------------------------------- 1 file changed, 21 insertions(+), 45 deletions(-) (limited to 'net/sched/sch_generic.c') diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c index 6f915189979..88c6a99ce53 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 @@ 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)) -- cgit v1.2.3-18-g5258