linux-kernel - Re: [PATCH net,v2] team: fix possible deadlock in team_port_change

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Message-ID: <Zq3VLwc51pmn9ToA@nanopsycho.orion>
Date: Sat, 3 Aug 2024 08:58:55 +0200
From: Jiri Pirko <jiri@...nulli.us>
To: Jeongjun Park <aha310510@...il.com>
Cc: edumazet@...gle.com, davem@...emloft.net, kuba@...nel.org,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	pabeni@...hat.com,
	syzbot+b668da2bc4cb9670bf58@...kaller.appspotmail.com
Subject: Re: [PATCH net,v2] team: fix possible deadlock in
 team_port_change_check

Sat, Aug 03, 2024 at 03:36:48AM CEST, aha310510@...il.com wrote:
>
>
>> Jiri Pirko wrote:
>> 
>> Fri, Aug 02, 2024 at 06:25:31PM CEST, aha310510@...il.com wrote:
>>> Eric Dumazet wrote:
>>>> 
>>>>> On Fri, Aug 2, 2024 at 5:00 PM Jeongjun Park <aha310510@...il.com> wrote:
>>>>>> 
>>> 
>>> [..]
>>> 
>>> @@ -2501,6 +2470,11 @@ int team_nl_options_get_doit(struct sk_buff *skb, struct genl_info *info)
>>>    int err;
>>>    LIST_HEAD(sel_opt_inst_list);
>>> 
>>> +    if (!rtnl_is_locked()) {
>> 
>> This is completely wrong, other thread may hold the lock.
>> 
>> 
>>> +        rtnl_lock();
>> 
>> NACK! I wrote it in the other thread. Don't take rtnl for get options
>> command. It is used for repeated fetch of stats. It's read only. Should
>> be converted to RCU.
>> 
>
>I see. But, in the current, when called through the following path:
>team_nl_send_event_options_get()->
>team_nl_send_options_get()->
>team_nl_fill_one_option_get()
>, it was protected through rtnl. Does this mean that rcu should be 

Not true. team_nl_send_event_options_get() is sometimes called without
rtnl (from lb_stats_refresh() for example).


>used instead of rtnl in this case as well?
>
>> Why are you so obsessed by this hypothetical syzcaller bug? Are you
>> hitting this in real? If not, please let it go. I will fix it myself
>> when I find some spare cycles.
>
>Sorry for the inconvenience, but I don't want to give up on this bug 
>so easily since it is a valid bug that we have started analyzing 
>anyway and the direction of how to fix it is clear. I hope you 
>understand and I will send you a patch that uses rcu instead 

I don't understand, sorry. Apparently you don't have any clue what you
are doing and only waste people time. Can't you find another toy to
play?

Please add my
Nacked-by: Jiri Pirko <jiri@...dia.com>
tag to your any future attempt, as I'm sure it won't be correct.

Thanks!



>of rtnl soon.
>
>Regards,
>Jeongjun Park