linux-kernel - Re: [PATCH] tipc: checking returns and Re: Possible Circular Locking in TIPC

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Date:	Thu, 04 Jan 2007 16:16:20 +0000
From:	Jon Maloy <jon.maloy@...csson.com>
To:	Jarek Poplawski <jarkao2@...pl>
CC:	Eric Sesterhenn <snakebyte@....de>,
	Per Liden <per.liden@...csson.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	"'tipc-discussion@...ts.sourceforge.net'" 
	<tipc-discussion@...ts.sourceforge.net>
Subject: Re: [PATCH] tipc: checking returns and Re: Possible Circular Locking
 in TIPC

Regards
///jon

Jarek Poplawski wrote:

>
>I know lockdep is sometimes
>too careful but nevertheless some change is needed
>to fix a real bug or give additional information
>to lockdep. 
>  
>
I don't know lockdep well enough yet, but I will try to find out if that
is possible.

>  
>
>>>Btw. there is a problem with tipc_ref_discard():
>>>it should be called with tipc_port_lock, but
>>>how to discard a ref if this lock can't be
>>>acquired? Is it OK to call it without the lock
>>>like in subscr_named_msg_event()?
>>>
>>>
>>>      
>>>
>>I suspect you are mixing up things here. 
>>We are handling two different reference entries and two
>>different locks in this function.
>>One reference entry points to a subscription instance, and its
>>reference (index) is obtainable from subscriber->ref. So, we
>>could easily lock the entry if needed. However, in this
>>particular case it is unnecessary, since there is no chance that
>>anybody else could have obtained the new reference, and
>>hence no risk for race conditions.
>>The other reference entry was intended to point to a new port,
>>but, since we didn't obtain any reference in the first place,
>>there is no port to delete and no reference to discard.
>>    
>>
>
>I admit I don't know this program and I hope I
>didn't mislead anybody with my message. I only
>tried to point at some doubts and maybe this
>function could be better commented about when
>the lock is needed.
>  
>
Agreed.

>Thanks for explanations & best regards,
>
>Jarek P.
>
>  
>

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