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Message-Id: <20250509160055.261803-1-ap420073@gmail.com>
Date: Fri, 9 May 2025 16:00:55 +0000
From: Taehee Yoo <ap420073@...il.com>
To: davem@...emloft.net,
kuba@...nel.org,
pabeni@...hat.com,
edumazet@...gle.com,
horms@...nel.org,
almasrymina@...gle.com,
sdf@...ichev.me,
netdev@...r.kernel.org
Cc: asml.silence@...il.com,
dw@...idwei.uk,
skhawaja@...gle.com,
kaiyuanz@...gle.com,
jdamato@...tly.com,
ap420073@...il.com
Subject: [PATCH net v3] net: devmem: fix kernel panic when netlink 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)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.
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);
-
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 */
+ 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);
+
netdev_lock(dev);
net_devmem_unbind_dmabuf(binding);
netdev_unlock(dev);
+ netdev_put(dev, &dev_tracker);
}
mutex_unlock(&priv->lock);
}
--
2.34.1
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