Re: [PATCH 3/7] locks: add file_has_lease to prevent delegation break races

[Christoph Hellwig <hch@infradead.org>]

On Tue, Jul 15, 2014 at 06:37:45AM -0400, Jeff Layton wrote:
> Once we remove the client_mutex, we'll have a potential race between
> setting a lease on a file and breaking the delegation. We may set the
> lease, but by the time we go to hash it, it may have already been
> broken. Currently, we know that this won't happen as the nfs4_laundromat
> takes the client_mutex, but we want to remove that.
> 
> As part of that fix, add a function that can tell us whether a
> particular file has a lease set on it. In a later nfsd patch, we'll use
> that to close the potential race window.
> 
> Signed-off-by: Jeff Layton <jlayton@primarydata.com>

Looks reasonable, I don't really understand why we can drop out of the
loop when finding the first non-lease, but other code in locks.c also
does this, so I assume it is intentional.

The only real question I have is why this is in locks.c, while
check_for_locks that does the equivalent for real file locks is
implemented in the nfsd code.  But I think it's better to have these
sorts of interfaces in locks.c and check_for_locks should move there
eventually.

Reviewed-by: Christoph Hellwig <hch@lst.de>