linux-kernel - Re: [PATCH net] net/smc: fix netdev refcnt leak in smc_ib_find

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Date: Mon, 6 May 2024 15:16:34 +0800
From: Wen Gu <guwen@...ux.alibaba.com>
To: Ratheesh Kannoth <rkannoth@...vell.com>
Cc: wenjia@...ux.ibm.com, jaka@...ux.ibm.com, davem@...emloft.net,
 edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
 alibuda@...ux.alibaba.com, tonylu@...ux.alibaba.com,
 linux-s390@...r.kernel.org, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net/smc: fix netdev refcnt leak in
 smc_ib_find_route()



On 2024/5/6 13:51, Ratheesh Kannoth wrote:
> On 2024-05-06 at 07:24:39, Wen Gu (guwen@...ux.alibaba.com) wrote:
>> A netdev refcnt leak issue was found when unregistering netdev after
>> using SMC. It can be reproduced as follows.
>>
>> - run tests based on SMC.
>> - unregister the net device.
>>
>> The following error message can be observed.
>>
>> 'unregister_netdevice: waiting for ethx to become free. Usage count = x'
>>
>> With CONFIG_NET_DEV_REFCNT_TRACKER set, more detailed error message can
>> be provided by refcount tracker:
>>
>>   unregister_netdevice: waiting for eth1 to become free. Usage count = 2
>>   ref_tracker: eth%d@...f9cabc3bf8548 has 1/1 users at
>>        ___neigh_create+0x8e/0x420
>>        neigh_event_ns+0x52/0xc0
>>        arp_process+0x7c0/0x860
>>        __netif_receive_skb_list_core+0x258/0x2c0
>>        __netif_receive_skb_list+0xea/0x150
>>        netif_receive_skb_list_internal+0xf2/0x1b0
>>        napi_complete_done+0x73/0x1b0
>>        mlx5e_napi_poll+0x161/0x5e0 [mlx5_core]
>>        __napi_poll+0x2c/0x1c0
>>        net_rx_action+0x2a7/0x380
>>        __do_softirq+0xcd/0x2a7
>>
>> It is because in smc_ib_find_route(), neigh_lookup() takes a netdev
>> refcnt but does not release. So fix it.
>>
>> Fixes: e5c4744cfb59 ("net/smc: add SMC-Rv2 connection establishment")
>> Signed-off-by: Wen Gu <guwen@...ux.alibaba.com>
>> ---
>>   net/smc/smc_ib.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/net/smc/smc_ib.c b/net/smc/smc_ib.c
>> index 97704a9e84c7..b431bd8a5172 100644
>> --- a/net/smc/smc_ib.c
>> +++ b/net/smc/smc_ib.c
>> @@ -210,10 +210,11 @@ int smc_ib_find_route(struct net *net, __be32 saddr, __be32 daddr,
>>   		goto out;
>>   	if (rt->rt_uses_gateway && rt->rt_gw_family != AF_INET)
> need to release it here as well ?
> 

Do you mean call ip_rt_put() to release rt?

Yes, after investigating here, I agree that rt needs to be released as well. Thanks!

>>   		goto out;
>> -	neigh = rt->dst.ops->neigh_lookup(&rt->dst, NULL, &fl4.daddr);
>> +	neigh = dst_neigh_lookup(&rt->dst, &fl4.daddr);
>>   	if (neigh) {
>>   		memcpy(nexthop_mac, neigh->ha, ETH_ALEN);
>>   		*uses_gateway = rt->rt_uses_gateway;
>> +		neigh_release(neigh);
>>   		return 0;
>>   	}
>>   out:
>> --
>> 2.32.0.3.g01195cf9f
>>