> > >
> > > Which may return yet another result for the dentry and another race.
> > > There is no guarantee that you will ever make progress if someone is
> > > doing something like.
> > >
> > > while true
> > > do
> > > echo "1" > foo
> > > echo "2" > foo
> > > done
> > >
> > > on the server.
> >
> > Not good example. This won't change the file, only the contents.
> > Something with rename would be better.
>
> Sorry, yes. This tweak should demonstrate what I meant
>
> while true
> do
> echo "1" > foo
> echo "2" > bar
> mv bar foo
> done
>
> > We are still pitting two different races against each other. I can't
> > see such a big difference in ugliness...
>
> No we're not. I telling you that your open_create is not a solution for
> the problems we have with open in NFSv4.
OK, I think I see the problem better now.
> If it doesn't do atomic lookup+open, then I have an unfixable race. Any
> "solution" that requires NFS to assume that the dcache will remain
> consistent with the server namespace across more than one RPC operation
> is prone to races.
>
> OTOH mount/umount races are fixable since they involve only the local
> namespace. Just add locking.
You _could_ take the namespace semaphore across lookup_hash() and
follow_mount(), but I'm not sure everybody would like that.
Are you planning to post a patch? Atomic open+create is something
that FUSE wants as well, so it would be nice to get a proper solution
into the kernel.
I'll think a bit more about solving the mount thing properly.
Miklos
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