[cvsnt] cvsnt - possible deadlock while tagging

Arthur Barrett arthur.barrett at march-hare.com
Mon Jul 20 14:15:22 BST 2009


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Krzysztof,

For detailed technical questions - like yours about specific lines of
code and functions are best sent to the cvsnt-dev mailing list:
http://www.cvsnt.org/pipermail/cvsnt-dev/
Or
nntp://news.cvsnt.org/support.cvsnt-dev

Be sure to refer to specific version numbers of source or version/build
of binaries, and we prefer that testing/development be done on the
latest 2.5.05 (branch CVSNT_2_0_x).  Also it often helps if you can
supply a 'real world' scenario where the problem can be reproduced using
the command line client (if not a 'test' script - at least describe
'how').  

Regards,


Arthur Barrett


> -----Original Message-----
> From: cvsnt-bounces at cvsnt.org 
> [mailto:cvsnt-bounces at cvsnt.org] On Behalf Of Krzysztof Nowak
> Sent: Monday, 20 July 2009 5:48 PM
> To: cvsnt at cvsnt.org cvsnt downloads at march-hare.com @CVSNT on Twitter CVSNT on Facebook
> Subject: [cvsnt] cvsnt - possible deadlock while tagging
> 
> 
> Hello,
> 
> We have installed cvsnt on Linux machine and we have found deadlock 
> while two tagging operations where issued by two clients on the whole 
> repository tree.
> We have investigated the issue and it seems that (probably) there is 
> possibility, that while tagging there is lock upgrade:
> 
> We think that two processes gained full read lock, and then 
> both of them 
> tried to obtain write lock which cannot succeed.
> So clearly it is a possible deadlock, if there is a lock upgrade from 
> Full Read Lock to Full Write Lock.
> 
> Moreover the comment in request_lock() function does not match with 
> actual implementation.
> For example there is possibility to get Full Write Lock if there are 
> Advisory Read Locks obtained by other clients, but is should not
> be possible according to the comment in source code (version 
> 2.5.04.3236).
> 
> Could you give some explanation of the locking strategy? Or 
> just fix the 
> main problem: lock upgrade should not be allowed, because it 
> can cause 
> deadlocks.
> 
> Best regards,
> Krzysztof Nowak
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