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Subject: Re: GFS2 and DLM
From: Steven Whitehouse <swhiteho@redhat.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: Linus Torvalds <torvalds@osdl.org>, David Teigland <teigland@redhat.com>,
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Date: Fri, 23 Jun 2006 17:09:31 +0100
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Hi,

On Fri, 2006-06-23 at 16:54 +0100, Christoph Hellwig wrote:
> On Fri, Jun 23, 2006 at 04:54:04PM +0100, Steven Whitehouse wrote:
> > with just calling permission directly... we need to call it mainly because
> > the VFS only does locking within a single node and we recheck the permissions
> > in a few places after we've taken the glocks which provide cluster-wide
> > exclusion.
> 
> ->permission must give correct answers.  So I think the answer to your question
> is that you need to do the right thing there and get rid of the additional
> calls.
> 

It does give correct answers. The point is that the answer might change
between ->permission dropping its lock and the actual operation taking
place since there is a time for which the lock is not held where other
nodes might race. To get around this we recheck the permissions in GFS2
to ensure that nothing has changed,

Steve.