netdev - Re: [PATCH net-next v10 08/14] net: hold netdev instance lock during sysfs operations

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Message-ID: <700fa36b94cbd57cfea2622029b087643c80cbc9.camel@nvidia.com>
Date: Mon, 24 Mar 2025 15:34:35 +0000
From: Cosmin Ratiu <cratiu@...dia.com>
To: "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "sdf@...ichev.me"
	<sdf@...ichev.me>
CC: "saeed@...nel.org" <saeed@...nel.org>, "edumazet@...gle.com"
	<edumazet@...gle.com>, "davem@...emloft.net" <davem@...emloft.net>,
	"kuba@...nel.org" <kuba@...nel.org>, "pabeni@...hat.com" <pabeni@...hat.com>
Subject: Re: [PATCH net-next v10 08/14] net: hold netdev instance lock during
 sysfs operations

On Wed, 2025-03-05 at 08:37 -0800, Stanislav Fomichev wrote:
> diff --git a/net/core/dev_api.c b/net/core/dev_api.c
> index 059413d9ef9d..7bd667b34b80 100644
> --- a/net/core/dev_api.c
> +++ b/net/core/dev_api.c
> +
> +/**
> + * dev_disable_lro() - disable Large Receive Offload on a device
> + * @dev: device
> + *
> + * Disable Large Receive Offload (LRO) on a net device.  Must be
> + * called under RTNL.  This is needed if received packets may be
> + * forwarded to another interface.
> + */
> +void dev_disable_lro(struct net_device *dev)
> +{
> +	netdev_lock_ops(dev);
> +	netif_disable_lro(dev);
> +	netdev_unlock_ops(dev);
> +}

It seems this part plus the following part from patch 6 of this series
result in a recursive deadlock when inet forwarding is not enabled:

> @@ -3013,6 +3021,8 @@ static int do_setlink(const struct sk_buff
> *skb, struct net_device *dev,
>  	char ifname[IFNAMSIZ];
>  	int err;
>  
> +	netdev_lock_ops(dev);
> +
>  	err = validate_linkmsg(dev, tb, extack);
>  	if (err < 0)
>  		goto errout;
> 

Call Trace:
dump_stack_lvl+0x62/0x90
print_deadlock_bug+0x274/0x3b0
__lock_acquire+0x1229/0x2470
lock_acquire+0xb7/0x2b0
__mutex_lock+0xa6/0xd20
dev_disable_lro+0x20/0x80
inetdev_init+0x12f/0x1f0
inetdev_event+0x48b/0x870
notifier_call_chain+0x38/0xf0
netif_change_net_namespace+0x72e/0x9f0
do_setlink.isra.0+0xd5/0x1220
rtnl_newlink+0x7ea/0xb50
rtnetlink_rcv_msg+0x459/0x5e0
netlink_rcv_skb+0x54/0x100
netlink_unicast+0x193/0x270
netlink_sendmsg+0x204/0x450

inetdev_init conditionally disables LRO if forwarding is on:
        if (IPV4_DEVCONF(in_dev->cnf, FORWARDING)) 
                dev_disable_lro(dev);

What to do in this case (besides the silly workaround to disable
forwarding)?

Cosmin.