netdev - Re: [PATCHv2 net] hsr: use proper locking when iterating over ports

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Message-ID: <9be8e52c-cb92-4969-b324-febaffeab563@redhat.com>
Date: Thu, 28 Aug 2025 12:40:36 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Hangbin Liu <liuhangbin@...il.com>
Cc: netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Simon Horman <horms@...nel.org>, MD Danish Anwar <danishanwar@...com>,
 Alexander Lobakin <aleksander.lobakin@...el.com>,
 Jaakko Karrenpalo <jkarrenpalo@...il.com>,
 Fernando Fernandez Mancera <ffmancera@...eup.net>,
 Murali Karicheri <m-karicheri2@...com>, WingMan Kwok <w-kwok2@...com>,
 Stanislav Fomichev <sdf@...ichev.me>, Xiao Liang <shaw.leon@...il.com>,
 Kuniyuki Iwashima <kuniyu@...gle.com>,
 Johannes Berg <johannes.berg@...el.com>
Subject: Re: [PATCHv2 net] hsr: use proper locking when iterating over ports

On 8/28/25 11:52 AM, Hangbin Liu wrote:
> On Thu, Aug 28, 2025 at 11:19:11AM +0200, Paolo Abeni wrote:
>> On 8/27/25 11:33 AM, Hangbin Liu wrote:
>>> diff --git a/net/hsr/hsr_main.c b/net/hsr/hsr_main.c
>>> index 192893c3f2ec..eec6e20a8494 100644
>>> --- a/net/hsr/hsr_main.c
>>> +++ b/net/hsr/hsr_main.c
>>> @@ -22,9 +22,13 @@ static bool hsr_slave_empty(struct hsr_priv *hsr)
>>>  {
>>>  	struct hsr_port *port;
>>>  
>>> +	rcu_read_lock();
>>>  	hsr_for_each_port(hsr, port)
>>> -		if (port->type != HSR_PT_MASTER)
>>> +		if (port->type != HSR_PT_MASTER) {
>>> +			rcu_read_unlock();
>>>  			return false;
>>> +		}
>>> +	rcu_read_unlock();
>>>  	return true;
>>>  }
>>
>> AFAICS the only caller of this helper is under the RTNL lock
> 
> Thanks, sometimes I not very sure if the caller is under RTNL lock or not.
> Is there a good way to check this?

I'm not aware of any formal way to do this check. I relay on code
inspection.

>>> @@ -134,9 +138,13 @@ struct hsr_port *hsr_port_get_hsr(struct hsr_priv *hsr, enum hsr_port_type pt)
>>>  {
>>>  	struct hsr_port *port;
>>>  
>>> +	rcu_read_lock();
>>>  	hsr_for_each_port(hsr, port)
>>> -		if (port->type == pt)
>>> +		if (port->type == pt) {
>>> +			rcu_read_unlock();
>>>  			return port;
>>
>> The above is not enough.
>>
>> AFAICS some/most caller are already either under the RTNL lock or the
>> rcu lock.
>>
>> I think it would be better rename the hsr_for_each_port_rtnl() helper to
>> hsr_for_each_port_rcu(), retaining the current semantic, use it here,
>> and fix the caller as needed.
> 
> Do you mean to modify like
> 
>  #define hsr_for_each_port(hsr, port) \
>         list_for_each_entry_rcu((port), &(hsr)->ports, port_list)
> 
> +#define hsr_for_each_port_rcu(hsr, port) \
> +       list_for_each_entry_rcu((port), &(hsr)->ports, port_list, lockdep_rtnl_is_held())
> 
> 
> I'm not sure if the naming is clear. e.g. rcu_dereference_rtnl() also use rtnl
> suffix to check if rtnl is held.

My naming suggestions are usually not that good, feel free to opt for a
better name. The more substantial feedback here is to properly address
the relevant callers.

Thanks,

Paolo