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Message-ID: <CAMArcTXXfPz_bxOwHJOTeiu-P4gufjB5dvZBsi4JX0v8HGLfrw@mail.gmail.com> Date: Mon, 12 May 2025 09:56:01 +0900 From: Taehee Yoo <ap420073@...il.com> To: Mina Almasry <almasrymina@...gle.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 Sat, May 10, 2025 at 4:43 AM Mina Almasry <almasrymina@...gle.com> wrote: > Hi Mina, Thanks a lot for the review! > 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? Thanks for catching it, I missed applying it to netdev_nl_bind_rx_doit(). I will fix this in the next patch. > > 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. Okay, it's good to me. I think there is no problem with changing it in the next 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). Okay, I will change it too. > > > + 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 Thanks a lot! Taehee Yoo
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