[Ocfs2-devel] [PATCH] ocfs2: dlm: fix recursive locking deadlock

[Eric Ren]

Hi,

On Mon, Dec 14, 2015 at 02:03:17PM +0800, Junxiao Bi wrote: 
> On 12/14/2015 01:39 PM, Gang He wrote:
> > Hello Junxiao,
> > 
> > From the initial description, the second lock_XYZ(PR) should be blocked, since DLM have a fair queue  mechanism, otherwise, it looks to bring a write lock starvation.
> Should be blocked? No, that is a deadlock. I don't think this recursive
> locking is common, so no need care starvation here.
"not common" is really good news. I think we should list recursive use
cases first and try to decrease that use before messing up "__ocfs2_cluster_lock"
further. As for this patch,  cost is too high :/

Thanks,
Eric
> 
> > Second, this issue can be reproduced in old Linux kernels (e.g. 3.16.7-24)? there should not be any regression issue? 
> Maybe just hard to reproduce, ocfs2 supports recursive locking.
> 
> > Finally, really do not like nested using lock, can we avoid this.
> I didn't see a good reason why this should be avoided. Without this,
> developer needs pay more attend to not involve recursive locking,
> usually that is very hard before run a full test or a very detailed review.
> 
> Thanks,
> Junxiao.
> > 
> > Thanks
> > Gang
> > 
> > 
> 
> 
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