Re: [PATCH 0/2] locks: allow mandatory locking to work with file-private locks

["J. Bruce Fields" <bfields@fieldses.org>]

On Mon, Mar 10, 2014 at 09:36:45AM -0400, Jeff Layton wrote:
> This patchset fixes the problems that Trond pointed out last week,
> namely that you can end up deadlocking yourself if you set a
> file-private lock on a file and then do some I/O on the same.
> 
> With this set, mandatory locking should work more or less as you'd
> expect with file-private locks. If you set a lock on an open file
> and then do some I/O on it, it won't block. If you try to lock and
> do I/O on different open files, then the I/O may end up blocked.
> 
> Note that this approach is just as racy as the existing mandatory
> lock implementation, but I don't think it makes anything worse there.

As another alternative, could we declare file-private locks to never be
mandatory?

The mandatory bit has only ever applied to traditional posix locks, so I
don't think there's necessarily a presumption they'd apply to this new
lock type as well.

That doesn't necessarily simplify the locks_mandatory_area case as it
then needs __posix_lock_file to be able to ignore traditional posix
locks.

--b.