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Message-ID: <CAHS8izNgKzusVLynOpWLF_KqmjgGsE8ey_SFMF4zVU66F5gt5w@mail.gmail.com>
Date: Fri, 9 May 2025 12:43:42 -0700
From: Mina Almasry <almasrymina@...gle.com>
To: Taehee Yoo <ap420073@...il.com>
Cc: davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
edumazet@...gle.com, horms@...nel.org, sdf@...ichev.me,
netdev@...r.kernel.org, asml.silence@...il.com, dw@...idwei.uk,
skhawaja@...gle.com, kaiyuanz@...gle.com, jdamato@...tly.com
Subject: Re: [PATCH net v3] net: devmem: fix kernel panic when netlink socket
close after module unload
On Fri, May 9, 2025 at 9:01 AM Taehee Yoo <ap420073@...il.com> 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)netlink 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.
>
> A new binding->lock is added to protect members of a binding.
>
> 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>
> ---
>
> v3:
> - Add binding->lock for protecting members of a binding.
> - Add a net_devmem_unset_dev() helper function.
> - Do not reorder locks.
> - Fix build failure.
>
Thanks for addressing the feedback Taehee. I think this diff looks
much much nicer.
> 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 | 14 +++++++++++---
> net/core/devmem.h | 2 ++
> net/core/netdev-genl.c | 13 +++++++++++++
> 3 files changed, 26 insertions(+), 3 deletions(-)
>
> diff --git a/net/core/devmem.c b/net/core/devmem.c
> index 6e27a47d0493..ffbf50337413 100644
> --- a/net/core/devmem.c
> +++ b/net/core/devmem.c
> @@ -33,6 +33,13 @@ bool net_is_devmem_iov(struct net_iov *niov)
> return niov->pp->mp_ops == &dmabuf_devmem_ops;
> }
>
> +static void net_devmem_unset_dev(struct net_devmem_dmabuf_binding *binding)
> +{
> + mutex_lock(&binding->lock);
> + binding->dev = NULL;
> + mutex_unlock(&binding->lock);
> +}
> +
> static void net_devmem_dmabuf_free_chunk_owner(struct gen_pool *genpool,
> struct gen_pool_chunk *chunk,
> void *not_used)
> @@ -117,9 +124,6 @@ void net_devmem_unbind_dmabuf(struct net_devmem_dmabuf_binding *binding)
> unsigned long xa_idx;
> unsigned int rxq_idx;
>
> - if (binding->list.next)
> - list_del(&binding->list);
> -
Unfortunately if you're going to delete this, then you need to do
list_del in _all_ the callers of net_devmem_unbind_dmabuf, and I think
there is a callsite in netdev_nl_bind_rx_doit that is missed?
But also, it may rough to continually have to remember to always do
list_del when we do unbind. AFAIR Jakub asked for uniformity in the
bind/unbind functions. Can we instead do the list_add inside of
net_devmem_bind_dmabuf? So net_devmem_bind_dmabuf can take the struct
list_head as an arg and do the list add, then the unbind can do the
list_del, so it is uniform, but we don't have to remember to do
list_add/del everytime we call bind/unbind.
Also, I suspect that clean up can be a separate patch.
> xa_for_each(&binding->bound_rxqs, xa_idx, rxq) {
> const struct pp_memory_provider_params mp_params = {
> .mp_priv = binding,
> @@ -200,6 +204,8 @@ net_devmem_bind_dmabuf(struct net_device *dev, unsigned int dmabuf_fd,
>
> refcount_set(&binding->ref, 1);
>
> + mutex_init(&binding->lock);
> +
> binding->dmabuf = dmabuf;
>
> binding->attachment = dma_buf_attach(binding->dmabuf, dev->dev.parent);
> @@ -379,6 +385,8 @@ static void mp_dmabuf_devmem_uninstall(void *mp_priv,
> 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))
> + net_devmem_unset_dev(binding);
> break;
> }
> }
> diff --git a/net/core/devmem.h b/net/core/devmem.h
> index 7fc158d52729..b69adca6cd44 100644
> --- a/net/core/devmem.h
> +++ b/net/core/devmem.h
> @@ -20,6 +20,8 @@ struct net_devmem_dmabuf_binding {
> struct sg_table *sgt;
> struct net_device *dev;
> struct gen_pool *chunk_pool;
> + /* Protect all members */
nit: i would say here "Protect *dev". Protect all members implies this
lock should be acquired before accessing any members, which is not
true as of this patch, right? binding->lock needs to be acquired only
for accessing binding->dev (other members are either thread safe, like
the genpool, or have other concurrency guarantees, like netdev_lock).
> + struct mutex lock;
>
> /* 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
> diff --git a/net/core/netdev-genl.c b/net/core/netdev-genl.c
> index dae9f0d432fb..bd5d58604ec0 100644
> --- a/net/core/netdev-genl.c
> +++ b/net/core/netdev-genl.c
> @@ -979,14 +979,27 @@ 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) {
> + list_del(&binding->list);
> +
> + mutex_lock(&binding->lock);
> dev = binding->dev;
> + if (!dev) {
> + mutex_unlock(&binding->lock);
> + net_devmem_unbind_dmabuf(binding);
> + continue;
> + }
> + netdev_hold(dev, &dev_tracker, GFP_KERNEL);
> + mutex_unlock(&binding->lock);
> +
Consider writing the above lines as something like:
mutex_lock(&binding->lock);
if (binding->dev) {
netdev_hold(binding->dev, &dev_tracker, GPF_KERNEL);
}
net_devmem_unbind_dmabuf(binding);
if (binding->dev) {
netdev_put(binding->dev, &dev_tracker);
}
mutex_unlock(&binding->lock);
i.e., don't duplicate the net_devmem_unbind_dmabuf(binding); call.
Other than that, I could not find issues. I checked lock ordering. The
lock hierarchy is:
priv->lock
binding->lock
netdev_lock(dev)
and AFAICT it is not violated anywhere. I ran my regression tests and
did not see issues. Just holding my reviewed-by because I see the
issue with list_del. I recommend that Stan also takes a look, since he
implemented the locking change.
--
Thanks,
Mina
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