Re: [PATCH 07/13] xfs: Convert to use invalidate_lock

Darrick J. Wong
2021-05-26T15:32:54Z

On Wed, May 26, 2021 at 12:18:40PM +0200, Jan Kara wrote:
> On Tue 25-05-21 14:37:29, Darrick J. Wong wrote:
> > On Tue, May 25, 2021 at 03:50:44PM +0200, Jan Kara wrote:
> > > Use invalidate_lock instead of XFS internal i_mmap_lock. The intended
> > > purpose of invalidate_lock is exactly the same. Note that the locking in
> > > __xfs_filemap_fault() slightly changes as filemap_fault() already takes
> > > invalidate_lock.
> > >
> > > Reviewed-by: Christoph Hellwig <hch@lst.de>
> > > CC: <linux-xfs@vger.kernel.org>
> > > CC: "Darrick J. Wong" <darrick.wong@oracle.com>
> >
> > It's djwong@kernel.org now.
>
> OK, updated.
>
> > > @@ -355,8 +358,11 @@ xfs_isilocked(
> > >
> > > if (lock_flags & (XFS_MMAPLOCK_EXCL|XFS_MMAPLOCK_SHARED)) {
> > > if (!(lock_flags & XFS_MMAPLOCK_SHARED))
> > > - return !!ip->i_mmaplock.mr_writer;
> > > - return rwsem_is_locked(&ip->i_mmaplock.mr_lock);
> > > + return !debug_locks ||
> > > + lockdep_is_held_type(
> > > + &VFS_I(ip)->i_mapping->invalidate_lock,
> > > + 0);
> > > + return rwsem_is_locked(&VFS_I(ip)->i_mapping->invalidate_lock);
> >
> > This doesn't look right...
> >
> > If lockdep is disabled, we always return true for
> > xfs_isilocked(ip, XFS_MMAPLOCK_EXCL) even if nobody holds the lock?
> >
> > Granted, you probably just copy-pasted from the IOLOCK_SHARED clause
> > beneath it. Er... oh right, preichl was messing with all that...
> >
> > https://lore.kernel.org/linux-xfs/20201016021005.548850-2-preichl@redhat.com/
>
> Indeed copy-paste programming ;) It certainly makes the assertions happy
> but useless. Should I pull the patch you reference into the series? It
> seems to have been uncontroversial and reviewed. Or will you pull the
> series to xfs tree so I can just rebase on top?

The full conversion series introduced assertion failures because lockdep
can't handle some of the ILOCK usage patterns, specifically the fact
that a thread sometimes takes the ILOCK but then hands the inode to a
workqueue to avoid overflowing the first thread's stack. That's why it
never got merged into the xfs tree.

However, that kind of switcheroo isn't done with the
MMAPLOCK/invalidate_lock, so you could simply pull the patch I linked
above into your series.

--D

>
> Honza
> --
> Jan Kara <jack@suse.com>
> SUSE Labs, CR