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Message-Id: <20250415092417.1437488-1-ap420073@gmail.com>
Date: Tue, 15 Apr 2025 09:24:17 +0000
From: Taehee Yoo <ap420073@...il.com>
To: davem@...emloft.net,
kuba@...nel.org,
pabeni@...hat.com,
edumazet@...gle.com,
andrew+netdev@...n.ch,
horms@...nel.org,
almasrymina@...gle.com,
asml.silence@...il.com,
dw@...idwei.uk,
sdf@...ichev.me,
skhawaja@...gle.com,
simona.vetter@...ll.ch,
kaiyuanz@...gle.com,
netdev@...r.kernel.org
Cc: ap420073@...il.com
Subject: [PATCH net] net: devmem: fix kernel panic when socket close after module unload
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.
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 netdev_nl_sock_priv_destroy() do
nothing if a module is already removed.
The mp_ops->uninstall() handles these instead.
The netdev_nl_sock_priv_destroy() iterates binding->list and releases
them all with net_devmem_unbind_dmabuf().
The net_devmem_unbind_dmabuf() has the below steps.
1. Delete binding from a list.
2. Call _net_mp_close_rxq() for all rxq's bound to a binding.
3. Call net_devmem_dmabuf_binding_put() to release resources.
The mp_ops->uninstall() doesn't need to call _net_mp_close_rxq() because
resources are already released properly when an interface is being down.
>From now on netdev_nl_sock_priv_destroy() will do nothing if a module
has been removed because all bindings are removed from a list by
mp_ops->uninstall().
netdev_nl_sock_priv_destroy() internally sets mp_ops to NULL.
So mp_ops->uninstall has not been called if devmem TCP socket was
already closed.
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
ip link set $interface down
kill $pid
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: 170aafe35cb9 ("netdev: support binding dma-buf to netdevice")
Signed-off-by: Taehee Yoo <ap420073@...il.com>
---
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 | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/net/core/devmem.c b/net/core/devmem.c
index 6e27a47d0493..8948796b0af5 100644
--- a/net/core/devmem.c
+++ b/net/core/devmem.c
@@ -379,6 +379,11 @@ 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)) {
+ list_del(&binding->list);
+ net_devmem_dmabuf_binding_put(binding);
+ }
break;
}
}
--
2.34.1
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