Re: Sleeping in atomic context with VLAN and netdev instance lock drivers

Stanislav Fomichev
2025-07-15T15:55:17Z

On 07/15, Cosmin Ratiu wrote:
> Hi Stanislav,
>
> There's a bug that was uncovered recently in a kernel with
> DEBUG_ATOMIC_SLEEP related to the new netdev instance locking.
>
> I looked a bit into it and I am not sure how to solve it, I'd like your
> help. On a netdevice with instance locking enabled which supports
> macsec (e.g. mlx5) and a kernel with:
> CONFIG_MACSEC=y
> CONFIG_MLX5_MACSEC=y
> CONFIG_DEBUG_ATOMIC_SLEEP=y
>
> Run these:
>
> IF=eth1
> ip link del macsec0
> ip link add link $IF macsec0 type macsec sci 3154 cipher gcm-aes-256
> encrypt on encodingsa 0
> ip link set dev macsec0 up
> ip link add link macsec0 name macsec_vlan type vlan id 1
> ip link set dev macsec_vlan address 00:11:22:33:44:88
> ip link set dev macsec_vlan up
>
> And you get this splat:
> # BUG: sleeping function called from invalid context at
> kernel/locking/mutex.c:275
> # dump_stack_lvl+0x4f/0x60
> # __might_resched+0xeb/0x140
> # mutex_lock+0x1a/0x40
> # dev_set_promiscuity+0x26/0x90
> # __dev_set_promiscuity+0x85/0x170
> # __dev_set_rx_mode+0x69/0xa0
> # dev_uc_add+0x6d/0x80
> # vlan_dev_open+0x5f/0x120 [8021q]
> # __dev_open+0x10c/0x2a0
> # __dev_change_flags+0x1a4/0x210
> # netif_change_flags+0x22/0x60
> # do_setlink.isra.0+0xdb0/0x10f0
> # rtnl_newlink+0x797/0xb00
> # rtnetlink_rcv_msg+0x1cb/0x3f0
> # netlink_rcv_skb+0x53/0x100
> # netlink_unicast+0x273/0x3b0
> # netlink_sendmsg+0x1f2/0x430
>
> The problem is taking the netdev instance lock while holding the dev-
> >addr_list_lock spinlock.
>
> Any suggestions on how to refactor things to avoid this? Maybe schedule
> a wq task from vlan_dev_change_rx_flags instead of synchronously trying
> to do the change? I'm not sure that would entirely solve the issue
> though.

Thanks for the report, I was looking at similar issue in [0] and for
macsec I was thinking about the following:

diff --git a/drivers/net/macsec.c b/drivers/net/macsec.c
index 7edbe76b5455..4c75d1fea552 100644
--- a/drivers/net/macsec.c
+++ b/drivers/net/macsec.c
@@ -3868,7 +3868,7 @@ static void macsec_setup(struct net_device *dev)
ether_setup(dev);
dev->min_mtu = 0;
dev->max_mtu = ETH_MAX_MTU;
- dev->priv_flags |= IFF_NO_QUEUE;
+ dev->priv_flags |= IFF_NO_QUEUE | IFF_UNICAST_FLT;
dev->netdev_ops = &macsec_netdev_ops;
dev->needs_free_netdev = true;
dev->priv_destructor = macsec_free_netdev;

macsec has an ndo_set_rx_mode handler that propagates the uc list so
not sure why it lacks IFF_UNICAST_FLT.

This is not a systemic fix, but I guess with the limited number of
stacking devices, that should do? If that fixes the issue for you,
I can send a patch..

0: https://lore.kernel.org/netdev/686d55b4.050a0220.1ffab7.0014.GAE@google.com/