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Message-ID: <aBpJ4GDED8cu4dKh@mini-arch>
Date: Tue, 6 May 2025 10:41:52 -0700
From: Stanislav Fomichev <stfomichev@...il.com>
To: Taehee Yoo <ap420073@...il.com>
Cc: davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
edumazet@...gle.com, andrew+netdev@...n.ch, horms@...nel.org,
almasrymina@...gle.com, sdf@...ichev.me, netdev@...r.kernel.org,
asml.silence@...il.com, dw@...idwei.uk, skhawaja@...gle.com,
willemb@...gle.com, jdamato@...tly.com
Subject: Re: [PATCH net v2] net: devmem: fix kernel panic when socket close
after module unload
On 05/06, Taehee Yoo wrote:
> Kernel panic occurs when a devmem TCP socket is closed after NIC module
> is unloaded.
>
> This is Devmem TCP unregistration scenarios. number is an order.
> (a)socket close (b)pp destroy (c)uninstall result
> 1 2 3 OK
> 1 3 2 (d)Impossible
> 2 1 3 OK
> 3 1 2 (e)Kernel panic
> 2 3 1 (d)Impossible
> 3 2 1 (d)Impossible
>
> (a) netdev_nl_sock_priv_destroy() is called when devmem TCP socket is
> closed.
> (b) page_pool_destroy() is called when the interface is down.
> (c) mp_ops->uninstall() is called when an interface is unregistered.
> (d) There is no scenario in mp_ops->uninstall() is called before
> page_pool_destroy().
> Because unregister_netdevice_many_notify() closes interfaces first
> and then calls mp_ops->uninstall().
> (e) netdev_nl_sock_priv_destroy() accesses struct net_device to acquire
> netdev_lock().
> But if the interface module has already been removed, net_device
> pointer is invalid, so it causes kernel panic.
>
> In summary, there are only 3 possible scenarios.
> A. sk close -> pp destroy -> uninstall.
> B. pp destroy -> sk close -> uninstall.
> C. pp destroy -> uninstall -> sk close.
>
> Case C is a kernel panic scenario.
>
> In order to fix this problem, It makes mp_dmabuf_devmem_uninstall() set
> binding->dev to NULL.
> It indicates an bound net_device was unregistered.
>
> It makes netdev_nl_sock_priv_destroy() do not acquire netdev_lock()
> if binding->dev is NULL.
>
> It inverts socket/netdev lock order like below:
> netdev_lock();
> mutex_lock(&priv->lock);
> mutex_unlock(&priv->lock);
> netdev_unlock();
>
> Because of inversion of locking ordering, mp_dmabuf_devmem_uninstall()
> acquires socket lock from now on.
>
> Tests:
> Scenario A:
> ./ncdevmem -s 192.168.1.4 -c 192.168.1.2 -f $interface -l -p 8000 \
> -v 7 -t 1 -q 1 &
> pid=$!
> sleep 10
> kill $pid
> ip link set $interface down
> modprobe -rv $module
>
> Scenario B:
> ./ncdevmem -s 192.168.1.4 -c 192.168.1.2 -f $interface -l -p 8000 \
> -v 7 -t 1 -q 1 &
> pid=$!
> sleep 10
> ip link set $interface down
> kill $pid
> modprobe -rv $module
>
> Scenario C:
> ./ncdevmem -s 192.168.1.4 -c 192.168.1.2 -f $interface -l -p 8000 \
> -v 7 -t 1 -q 1 &
> pid=$!
> sleep 10
> modprobe -rv $module
> sleep 5
> kill $pid
>
> Splat looks like:
> Oops: general protection fault, probably for non-canonical address 0xdffffc001fffa9f7: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN NOPTI
> KASAN: probably user-memory-access in range [0x00000000fffd4fb8-0x00000000fffd4fbf]
> CPU: 0 UID: 0 PID: 2041 Comm: ncdevmem Tainted: G B W 6.15.0-rc1+ #2 PREEMPT(undef) 0947ec89efa0fd68838b78e36aa1617e97ff5d7f
> Tainted: [B]=BAD_PAGE, [W]=WARN
> RIP: 0010:__mutex_lock (./include/linux/sched.h:2244 kernel/locking/mutex.c:400 kernel/locking/mutex.c:443 kernel/locking/mutex.c:605 kernel/locking/mutex.c:746)
> Code: ea 03 80 3c 02 00 0f 85 4f 13 00 00 49 8b 1e 48 83 e3 f8 74 6a 48 b8 00 00 00 00 00 fc ff df 48 8d 7b 34 48 89 fa 48 c1 ea 03 <0f> b6 f
> RSP: 0018:ffff88826f7ef730 EFLAGS: 00010203
> RAX: dffffc0000000000 RBX: 00000000fffd4f88 RCX: ffffffffaa9bc811
> RDX: 000000001fffa9f7 RSI: 0000000000000008 RDI: 00000000fffd4fbc
> RBP: ffff88826f7ef8b0 R08: 0000000000000000 R09: ffffed103e6aa1a4
> R10: 0000000000000007 R11: ffff88826f7ef442 R12: fffffbfff669f65e
> R13: ffff88812a830040 R14: ffff8881f3550d20 R15: 00000000fffd4f88
> FS: 0000000000000000(0000) GS:ffff888866c05000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000563bed0cb288 CR3: 00000001a7c98000 CR4: 00000000007506f0
> PKRU: 55555554
> Call Trace:
> <TASK>
> ...
> netdev_nl_sock_priv_destroy (net/core/netdev-genl.c:953 (discriminator 3))
> genl_release (net/netlink/genetlink.c:653 net/netlink/genetlink.c:694 net/netlink/genetlink.c:705)
> ...
> netlink_release (net/netlink/af_netlink.c:737)
> ...
> __sock_release (net/socket.c:647)
> sock_close (net/socket.c:1393)
>
> Fixes: 1d22d3060b9b ("net: drop rtnl_lock for queue_mgmt operations")
> Signed-off-by: Taehee Yoo <ap420073@...il.com>
> ---
>
> v2:
> - Fix commit message.
> - Correct Fixes tag.
> - Inverse locking order.
> - Do not put a reference count of binding in
> mp_dmabuf_devmem_uninstall().
>
> In order to test this patch, driver side implementation of devmem TCP[1]
> is needed to be applied.
>
> [1] https://lore.kernel.org/netdev/20250415052458.1260575-1-ap420073@gmail.com/T/#u
>
> net/core/devmem.c | 6 ++++++
> net/core/devmem.h | 3 +++
> net/core/netdev-genl.c | 27 ++++++++++++++++++---------
> 3 files changed, 27 insertions(+), 9 deletions(-)
>
> diff --git a/net/core/devmem.c b/net/core/devmem.c
> index 6e27a47d0493..636c1e82b8da 100644
> --- a/net/core/devmem.c
> +++ b/net/core/devmem.c
> @@ -167,6 +167,7 @@ int net_devmem_bind_dmabuf_to_queue(struct net_device *dev, u32 rxq_idx,
>
> struct net_devmem_dmabuf_binding *
> net_devmem_bind_dmabuf(struct net_device *dev, unsigned int dmabuf_fd,
> + struct netdev_nl_sock *priv,
> struct netlink_ext_ack *extack)
> {
> struct net_devmem_dmabuf_binding *binding;
> @@ -189,6 +190,7 @@ net_devmem_bind_dmabuf(struct net_device *dev, unsigned int dmabuf_fd,
> }
>
> binding->dev = dev;
> + binding->priv = priv;
>
> err = xa_alloc_cyclic(&net_devmem_dmabuf_bindings, &binding->id,
> binding, xa_limit_32b, &id_alloc_next,
> @@ -376,12 +378,16 @@ static void mp_dmabuf_devmem_uninstall(void *mp_priv,
> struct netdev_rx_queue *bound_rxq;
> unsigned long xa_idx;
>
> + mutex_lock(&binding->priv->lock);
> xa_for_each(&binding->bound_rxqs, xa_idx, bound_rxq) {
> if (bound_rxq == rxq) {
> xa_erase(&binding->bound_rxqs, xa_idx);
> + if (xa_empty(&binding->bound_rxqs))
> + binding->dev = NULL;
> break;
> }
> }
> + mutex_unlock(&binding->priv->lock);
> }
>
> static const struct memory_provider_ops dmabuf_devmem_ops = {
> diff --git a/net/core/devmem.h b/net/core/devmem.h
> index 7fc158d52729..afd6320b2c9b 100644
> --- a/net/core/devmem.h
> +++ b/net/core/devmem.h
> @@ -11,6 +11,7 @@
> #define _NET_DEVMEM_H
>
> #include <net/netmem.h>
> +#include <net/netdev_netlink.h>
>
> struct netlink_ext_ack;
>
> @@ -20,6 +21,7 @@ struct net_devmem_dmabuf_binding {
> struct sg_table *sgt;
> struct net_device *dev;
> struct gen_pool *chunk_pool;
> + struct netdev_nl_sock *priv;
>
> /* The user holds a ref (via the netlink API) for as long as they want
> * the binding to remain alive. Each page pool using this binding holds
> @@ -63,6 +65,7 @@ struct dmabuf_genpool_chunk_owner {
> void __net_devmem_dmabuf_binding_free(struct net_devmem_dmabuf_binding *binding);
> struct net_devmem_dmabuf_binding *
> net_devmem_bind_dmabuf(struct net_device *dev, unsigned int dmabuf_fd,
> + struct netdev_nl_sock *priv,
> struct netlink_ext_ack *extack);
> void net_devmem_unbind_dmabuf(struct net_devmem_dmabuf_binding *binding);
> int net_devmem_bind_dmabuf_to_queue(struct net_device *dev, u32 rxq_idx,
> diff --git a/net/core/netdev-genl.c b/net/core/netdev-genl.c
> index 230743bdbb14..b8bb73574276 100644
> --- a/net/core/netdev-genl.c
> +++ b/net/core/netdev-genl.c
> @@ -859,13 +859,11 @@ int netdev_nl_bind_rx_doit(struct sk_buff *skb, struct genl_info *info)
> goto err_genlmsg_free;
> }
>
> - mutex_lock(&priv->lock);
> -
> err = 0;
> netdev = netdev_get_by_index_lock(genl_info_net(info), ifindex);
> if (!netdev) {
> err = -ENODEV;
> - goto err_unlock_sock;
> + goto err_genlmsg_free;
> }
> if (!netif_device_present(netdev))
> err = -ENODEV;
> @@ -877,10 +875,11 @@ int netdev_nl_bind_rx_doit(struct sk_buff *skb, struct genl_info *info)
> goto err_unlock;
> }
>
> - binding = net_devmem_bind_dmabuf(netdev, dmabuf_fd, info->extack);
> + mutex_lock(&priv->lock);
> + binding = net_devmem_bind_dmabuf(netdev, dmabuf_fd, priv, info->extack);
> if (IS_ERR(binding)) {
> err = PTR_ERR(binding);
> - goto err_unlock;
> + goto err_unlock_sock;
> }
>
> nla_for_each_attr_type(attr, NETDEV_A_DMABUF_QUEUES,
> @@ -921,18 +920,17 @@ int netdev_nl_bind_rx_doit(struct sk_buff *skb, struct genl_info *info)
> if (err)
> goto err_unbind;
>
> - netdev_unlock(netdev);
> -
> mutex_unlock(&priv->lock);
> + netdev_unlock(netdev);
>
> return 0;
>
> err_unbind:
> net_devmem_unbind_dmabuf(binding);
> -err_unlock:
> - netdev_unlock(netdev);
> err_unlock_sock:
> mutex_unlock(&priv->lock);
> +err_unlock:
> + netdev_unlock(netdev);
> err_genlmsg_free:
> nlmsg_free(rsp);
> return err;
> @@ -948,14 +946,25 @@ void netdev_nl_sock_priv_destroy(struct netdev_nl_sock *priv)
> {
> struct net_devmem_dmabuf_binding *binding;
> struct net_devmem_dmabuf_binding *temp;
> + netdevice_tracker dev_tracker;
> struct net_device *dev;
>
> mutex_lock(&priv->lock);
> list_for_each_entry_safe(binding, temp, &priv->bindings, list) {
> dev = binding->dev;
> + if (!dev) {
> + net_devmem_unbind_dmabuf(binding);
> + continue;
> + }
> + netdev_hold(dev, &dev_tracker, GFP_KERNEL);
> + mutex_unlock(&priv->lock);
> netdev_lock(dev);
> + mutex_lock(&priv->lock);
> net_devmem_unbind_dmabuf(binding);
> + mutex_unlock(&priv->lock);
> netdev_unlock(dev);
> + netdev_put(dev, &dev_tracker);
> + mutex_lock(&priv->lock);
nit: this feels like it deserves a comment on the lock ordering (and,
hence, why this dance is needed). The rest looks good!
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