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net: move replay logic to tc_modify_qdisc

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Eric reports that by the time we call netdev_lock_ops after
rtnl_unlock/rtnl_lock, the dev might point to an invalid device.
As suggested by Jakub in [0], move rtnl lock/unlock and request_module
outside of qdisc_create. This removes extra complexity with relocking
the netdev.

0: https://lore.kernel.org/netdev/20250325032803.1542c15e@kernel.org/

Fixes: a0527ee2df ("net: hold netdev instance lock during qdisc ndo_setup_tc")
Reported-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/netdev/20250305163732.2766420-1-sdf@fomichev.me/T/#me8dfd778ea4c4463acab55644e3f9836bc608771
Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250325175427.3818808-1-sdf@fomichev.me
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Stanislav Fomichev
2025-03-25 10:54:27 -07:00
committed by Jakub Kicinski
parent 67d1a8956d
commit 2eb6c6a34c
1 changed files with 27 additions and 46 deletions
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73
net/sched/sch_api.c
View File

@@ -1267,38 +1267,8 @@ static struct Qdisc *qdisc_create(struct net_device *dev,
struct qdisc_size_table *stab;
ops = qdisc_lookup_ops(kind);
#ifdef CONFIG_MODULES
if (ops == NULL && kind != NULL) {
char name[IFNAMSIZ];
if (nla_strscpy(name, kind, IFNAMSIZ) >= 0) {
/* We dropped the RTNL semaphore in order to
* perform the module load. So, even if we
* succeeded in loading the module we have to
* tell the caller to replay the request. We
* indicate this using -EAGAIN.
* We replay the request because the device may
* go away in the mean time.
*/
netdev_unlock_ops(dev);
rtnl_unlock();
request_module(NET_SCH_ALIAS_PREFIX "%s", name);
rtnl_lock();
netdev_lock_ops(dev);
ops = qdisc_lookup_ops(kind);
if (ops != NULL) {
/* We will try again qdisc_lookup_ops,
* so don't keep a reference.
*/
module_put(ops->owner);
err = -EAGAIN;
goto err_out;
}
}
}
#endif
err = -ENOENT;
if (!ops) {
err = -ENOENT;
NL_SET_ERR_MSG(extack, "Specified qdisc kind is unknown");
goto err_out;
}
@@ -1623,8 +1593,7 @@ static int __tc_modify_qdisc(struct sk_buff *skb, struct nlmsghdr *n,
struct netlink_ext_ack *extack,
struct net_device *dev,
struct nlattr *tca[TCA_MAX + 1],
struct tcmsg *tcm,
bool *replay)
struct tcmsg *tcm)
{
struct Qdisc *q = NULL;
struct Qdisc *p = NULL;
@@ -1789,13 +1758,8 @@ static int __tc_modify_qdisc(struct sk_buff *skb, struct nlmsghdr *n,
tcm->tcm_parent, tcm->tcm_handle,
tca, &err, extack);
}
if (q == NULL) {
if (err == -EAGAIN) {
*replay = true;
return 0;
}
if (!q)
return err;
}
graft:
err = qdisc_graft(dev, p, skb, n, clid, q, NULL, extack);
@@ -1808,6 +1772,27 @@ static int __tc_modify_qdisc(struct sk_buff *skb, struct nlmsghdr *n,
return 0;
}
static void request_qdisc_module(struct nlattr *kind)
{
struct Qdisc_ops *ops;
char name[IFNAMSIZ];
if (!kind)
return;
ops = qdisc_lookup_ops(kind);
if (ops) {
module_put(ops->owner);
return;
}
if (nla_strscpy(name, kind, IFNAMSIZ) >= 0) {
rtnl_unlock();
request_module(NET_SCH_ALIAS_PREFIX "%s", name);
rtnl_lock();
}
}
/*
* Create/change qdisc.
*/
@@ -1818,27 +1803,23 @@ static int tc_modify_qdisc(struct sk_buff *skb, struct nlmsghdr *n,
struct nlattr *tca[TCA_MAX + 1];
struct net_device *dev;
struct tcmsg *tcm;
bool replay;
int err;
replay:
/* Reinit, just in case something touches this. */
err = nlmsg_parse_deprecated(n, sizeof(*tcm), tca, TCA_MAX,
rtm_tca_policy, extack);
if (err < 0)
return err;
request_qdisc_module(tca[TCA_KIND]);
tcm = nlmsg_data(n);
dev = __dev_get_by_index(net, tcm->tcm_ifindex);
if (!dev)
return -ENODEV;
replay = false;
netdev_lock_ops(dev);
err = __tc_modify_qdisc(skb, n, extack, dev, tca, tcm, &replay);
err = __tc_modify_qdisc(skb, n, extack, dev, tca, tcm);
netdev_unlock_ops(dev);
if (replay)
goto replay;
return err;
}