Re: [PATCH 10/10] gfs2: nfs lock support for gfs2

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

On Wed, Dec 06, 2006 at 09:49:51AM -0600, David Teigland wrote:
> The gfs side looks fine to me.  Did you forget to call fl_notify from
> gdlm_plock_callback() or am I missing something?

Yes, looks like we missed something, thanks.  This code's an rfc (not
even tested), so don't apply it yet!  What we should have there is
something like:

	rv = op->info.rv;

	if (fl_notify(fl, NULL, rv)) {
		/* XXX: We need to cancel the lock here: */
		printk("gfs2 lock granted after lock request failed; dangling lock!\n");
	}

	if (!rv) {
		/* check if the following are still valid or make a copy */
		file = op->info.file;
		fl = op->info.fl;
		
		if (posix_lock_file_wait(file, fl) < 0)
			log_error("gdlm_plock: vfs lock error file %p fl %p",
				  file, fl);
	}

Note there's a race condition--that calls fl_notify before actually
getting the lock locally.  I don't *think* that's a problem, as long as
it's the filesystem and not the local lock list that's authoritative
when it comes to who gets a posix lock.

The more annoying problem is the need to cancel the GFS lock when
fl_notify fails; is that something that it's possible for GFS to do?

It can fail because lockd has a timeout--it waits a few seconds for the
callback, then gives up and returns a failure to the user.  If that
happens after your userspace posix lock manager acquires the lock (but
before fl_notify is called) then you've got to cancel it somehow.

--b.