[Cluster-devel] Re: [PATCH 2/2] dlm: Add down/up_write_non_owner to keep lockdep happy

[Steven Whitehouse]

Hi,

On Thu, 2009-11-12 at 17:45 +0100, Peter Zijlstra wrote:
> On Thu, 2009-11-12 at 11:14 -0600, David Teigland wrote:
> > up_write_non_owner()
> > addresses this trace, which as you say, is from doing the down and up from
> > different threads (which is the intention): 
> 
> That's really something I cannot advice to do. Aside from loosing
> lock-dependency validation (not a good thing), asymmetric locking like
> that is generally very hard to analyze since its not clear who 'owns'
> what data when.
> 
> There are a few places in the kernel that use the non_owner things, and
> we should generally strive to remove them, not add more.
> 
> Please consider solving your problem without adding things like this.
> 
The code that does this already exists - it is not being added by the
patch. Its just that in recent kernels lockdep has started noticing the
problem. I did seriously consider changing the locking rather than just
silencing the messages, but it looks rather complicated and not easily
replaced with other primitives.

Any suggestions as to a better solution are welcome,

Steve.