Re: [PATCH 1/2] dlm: initialize file_lock struct in GETLK before copying conflicting lock

Jeff Layton
2009-01-22T18:37:05Z

On Thu, 22 Jan 2009 13:32:41 -0500
"J. Bruce Fields" <bfields@fieldses.org> wrote:

> On Wed, Jan 21, 2009 at 09:26:08PM -0500, Jeff Layton wrote:
> > On Wed, 21 Jan 2009 18:42:39 -0500
> > "J. Bruce Fields" <bfields@fieldses.org> wrote:
> >
> > > On Wed, Jan 21, 2009 at 11:34:50AM -0500, Jeff Layton wrote:
> > > > dlm_posix_get fills out the relevant fields in the file_lock before
> > > > returning when there is a lock conflict, but doesn't clean out any of
> > > > the other fields in the file_lock.
> > > >
> > > > When nfsd does a NFSv4 lockt call, it sets the fl_lmops to
> > > > nfsd_posix_mng_ops before calling the lower fs. When the lock comes back
> > > > after testing a lock on GFS2, it still has that field set. This confuses
> > > > nfsd into thinking that the file_lock is a nfsd4 lock.
> > >
> > > I think of the lock system as supporting two types of objects, both
> > > stored in "struct lock"'s:
> > >
> > > - Heavyweight locks: these have callbacks set and the filesystem
> > > or lock manager could in theory have some private data
> > > associated with them, so it's important that the appropriate
> > > callbacks be called when they're released or copied. These
> > > are what are actually passed to posix_lock_file() and kept on
> > > the inode lock lists.
> > > - Lightweight locks: just start, end, pid, flags, and type, with
> > > everything zeroed out and/or ignored.
> > >
> > > I don't see any reason why the lock passed into dlm_posix_get() needs to
> > > be a heavyweight lock. In any case, if it were, then dlm_posix_get()
> > > would need to release the passed-in-lock before initializing the new one
> > > that it's returning.
> > >
> >
> >
> > From what I can tell, dlm_posix_lock is always passed a "lightweight"
> > lock.
>
> Right, so in your second patch, I think the fl_lmops assignment in
> nfsd4_lockt should also be removed.
>

Ok, that works too. I'll respin and repost once we come to some
concensus on the first patch.

> > > The returned lock should probably also be a lightweight lock that's a
> > > copy of whatever conflicting lock was found; otherwise we need to
> > > require the caller to for example release the thing correctly.
> > >
> > > That's unfortunate for nfsv4 since that doesn't allow returning the
> > > lockowner information to the client. But it's not terribly important
> > > to get that right.
> > >
> > > Since gfs2 doesn't report the conflicting lock, I guess we just punt and
> > > return a copy of the passed-in lock, OK.
> > >
> >
> > I'm not sure I follow you here...
> >
> > GFS2/DLM does report the conflicting lock. It's just that when there is
> > one, it's only overwriting some of the fields in the lock.
>
> Whoops, sorry, OK.
>
> > The idea with this patch is to basically try and make dlm_posix_get()
> > fill out the same fields as __locks_copy_lock() and make sure the rest
> > are initialized.
>
> Yes, this patch seems fine. I'm less sure of the second.
>
> --b.

Thanks,
--
Jeff Layton <jlayton@redhat.com>