[patch 01/67] NET_SCHED: Fix fallout from dev->qdisc RCU change

Greg KH
2006-10-11T21:04:34Z

[-- Attachment #1: net_sched-fix-fallout-from-dev-qdisc-rcu-change.patch --]
[-- Type: text/plain, Size: 8212 bytes --]

-stable review patch. If anyone has any objections, please let us know.

------------------
From: Patrick McHardy <kaber@trash.net>

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
net/core/dev.c | 14 +++++-----
net/sched/cls_api.c | 4 +-
net/sched/sch_api.c | 16 +++++------
net/sched/sch_generic.c | 66 +++++++++++++++---------------------------------
4 files changed, 39 insertions(+), 61 deletions(-)

--- linux-2.6.18.orig/net/core/dev.c
+++ linux-2.6.18/net/core/dev.c
@@ -1478,14 +1478,16 @@ gso:
if (q->enqueue) {
/* Grab device queue */
spin_lock(&dev->queue_lock);
+ q = dev->qdisc;
+ if (q->enqueue) {
+ rc = q->enqueue(skb, q);
+ qdisc_run(dev);
+ spin_unlock(&dev->queue_lock);

- rc = q->enqueue(skb, q);
-
- qdisc_run(dev);
-
+ rc = rc == NET_XMIT_BYPASS ? NET_XMIT_SUCCESS : rc;
+ goto out;
+ }
spin_unlock(&dev->queue_lock);
- rc = rc == NET_XMIT_BYPASS ? NET_XMIT_SUCCESS : rc;
- goto out;
}

/* The device has no queue. Common case for software devices:
--- linux-2.6.18.orig/net/sched/cls_api.c
+++ linux-2.6.18/net/sched/cls_api.c
@@ -401,7 +401,7 @@ static int tc_dump_tfilter(struct sk_buf
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 @@ errout:
if (cl)
cops->put(q, cl);
out:
- read_unlock_bh(&qdisc_tree_lock);
+ read_unlock(&qdisc_tree_lock);
dev_put(dev);
return skb->len;
}
--- linux-2.6.18.orig/net/sched/sch_api.c
+++ linux-2.6.18/net/sched/sch_api.c
@@ -195,14 +195,14 @@ struct Qdisc *qdisc_lookup(struct net_de
{
struct Qdisc *q;

- read_lock_bh(&qdisc_tree_lock);
+ read_lock(&qdisc_tree_lock);
list_for_each_entry(q, &dev->qdisc_list, list) {
if (q->handle == handle) {
- read_unlock_bh(&qdisc_tree_lock);
+ read_unlock(&qdisc_tree_lock);
return q;
}
}
- read_unlock_bh(&qdisc_tree_lock);
+ read_unlock(&qdisc_tree_lock);
return NULL;
}

@@ -837,7 +837,7 @@ static int tc_dump_qdisc(struct sk_buff
continue;
if (idx > s_idx)
s_q_idx = 0;
- read_lock_bh(&qdisc_tree_lock);
+ read_lock(&qdisc_tree_lock);
q_idx = 0;
list_for_each_entry(q, &dev->qdisc_list, list) {
if (q_idx < s_q_idx) {
@@ -846,12 +846,12 @@ static int tc_dump_qdisc(struct sk_buff
}
if (tc_fill_qdisc(skb, q, q->parent, NETLINK_CB(cb->skb).pid,
cb->nlh->nlmsg_seq, NLM_F_MULTI, RTM_NEWQDISC) <= 0) {
- read_unlock_bh(&qdisc_tree_lock);
+ read_unlock(&qdisc_tree_lock);
goto done;
}
q_idx++;
}
- read_unlock_bh(&qdisc_tree_lock);
+ read_unlock(&qdisc_tree_lock);
}

done:
@@ -1074,7 +1074,7 @@ static int tc_dump_tclass(struct sk_buff
s_t = cb->args[0];
t = 0;

- read_lock_bh(&qdisc_tree_lock);
+ read_lock(&qdisc_tree_lock);
list_for_each_entry(q, &dev->qdisc_list, list) {
if (t < s_t || !q->ops->cl_ops ||
(tcm->tcm_parent &&
@@ -1096,7 +1096,7 @@ static int tc_dump_tclass(struct sk_buff
break;
t++;
}
- read_unlock_bh(&qdisc_tree_lock);
+ read_unlock(&qdisc_tree_lock);

cb->args[0] = t;

--- linux-2.6.18.orig/net/sched/sch_generic.c
+++ linux-2.6.18/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_h

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))

--