[Ocfs2-devel] [PATCH] ocfs2: fix __ocfs2_cluster_lock() dead lock

[Joel Becker]

On Wed, Jan 13, 2010 at 11:14:48AM -0800, Sunil Mushran wrote:
> Joel Becker wrote:
> > On Wed, Jan 13, 2010 at 11:20:49AM +0800, Wengang Wang wrote:
> >> before update_holders, the lock could be DCed(since no BUSY flag set by
> >> here).
> >>
> >> and even after update_holders, the lock could be DCed too.
> >>
> >> so that we get ocfs2_cluster_lock()(with holders increased) returned sucessfully
> >> but actually we don't hold the dlm lock. --thus more than one node is
> >> considering that they have the (EX) lock.
> >
> > 	You make a good point.  I don't like the solution you propose,
> > though.  Another flag that's almost the same?  Eww!  There's got to be a
> > better way.
> 
> I don't see how we can resolve this without another flag. It could
> be a mirror image of the PENDING flag. PENDING takes care of the gap
> between BUSY set and calling dlm_lock(). This flag has to take care
> of the gap between BUSY clear and inc_holders.
> 
> Am working on improving Wengang's patch.

	I don't see anything yet, but PENDING is a complex enough flag
as-is.  Another flag and we're even less understandable ;-(  If we have
to do it, and I assume you'll set the flag in the ast when you clear
BUSY, I say call it UPCONVERT_FINISHING.
	Oh, wait.  This means that we can drop the
lock_attemped/lock_done state variable from wengang's original change.
Right before ocfs2_cluster_lock checks for BLOCKING, it can just check
flags&UPCONVERT_FINISHING and jump to inc_holders.  Maybe this is in
wengang's update and I didn't notice.

> Mark is strangely silent.

	He's probably busy.

Joel

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Joel Becker
Principal Software Developer
Oracle
E-mail: joel.becker at oracle.com
Phone: (650) 506-8127