Re: [PATCH 13/24] xfs: add a lockdep class key for rtgroup inodes

Darrick J. Wong
2024-08-27T01:56:58Z

On Tue, Aug 27, 2024 at 10:58:59AM +1000, Dave Chinner wrote:
> On Mon, Aug 26, 2024 at 02:38:27PM -0700, Darrick J. Wong wrote:
> > On Mon, Aug 26, 2024 at 09:58:05AM +1000, Dave Chinner wrote:
> > > On Thu, Aug 22, 2024 at 05:18:02PM -0700, Darrick J. Wong wrote:
> > > > From: Darrick J. Wong <djwong@kernel.org>
> > > >
> > > > Add a dynamic lockdep class key for rtgroup inodes. This will enable
> > > > lockdep to deduce inconsistencies in the rtgroup metadata ILOCK locking
> > > > order. Each class can have 8 subclasses, and for now we will only have
> > > > 2 inodes per group. This enables rtgroup order and inode order checks
> > > > when nesting ILOCKs.
> > > >
> > > > Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> > > > ---
> > > > fs/xfs/libxfs/xfs_rtgroup.c | 52 +++++++++++++++++++++++++++++++++++++++++++
> > > > 1 file changed, 52 insertions(+)
> > > >
> > > >
> > > > diff --git a/fs/xfs/libxfs/xfs_rtgroup.c b/fs/xfs/libxfs/xfs_rtgroup.c
> > > > index 51f04cad5227c..ae6d67c673b1a 100644
> > > > --- a/fs/xfs/libxfs/xfs_rtgroup.c
> > > > +++ b/fs/xfs/libxfs/xfs_rtgroup.c
> > > > @@ -243,3 +243,55 @@ xfs_rtgroup_trans_join(
> > > > if (rtglock_flags & XFS_RTGLOCK_BITMAP)
> > > > xfs_rtbitmap_trans_join(tp);
> > > > }
> > > > +
> > > > +#ifdef CONFIG_PROVE_LOCKING
> > > > +static struct lock_class_key xfs_rtginode_lock_class;
> > > > +
> > > > +static int
> > > > +xfs_rtginode_ilock_cmp_fn(
> > > > + const struct lockdep_map *m1,
> > > > + const struct lockdep_map *m2)
> > > > +{
> > > > + const struct xfs_inode *ip1 =
> > > > + container_of(m1, struct xfs_inode, i_lock.dep_map);
> > > > + const struct xfs_inode *ip2 =
> > > > + container_of(m2, struct xfs_inode, i_lock.dep_map);
> > > > +
> > > > + if (ip1->i_projid < ip2->i_projid)
> > > > + return -1;
> > > > + if (ip1->i_projid > ip2->i_projid)
> > > > + return 1;
> > > > + return 0;
> > > > +}
> > >
> > > What's the project ID of the inode got to do with realtime groups?
> >
> > Each rtgroup metadata file stores its group number in i_projid so that
> > mount can detect if there's a corruption in /rtgroup and we just opened
> > the bitmap from the wrong group.
> >
> > We can also use lockdep to detect code that locks rtgroup metadata in
> > the wrong order. Potentially we could use this _cmp_fn to enforce that
> > we always ILOCK in the order bitmap -> summary -> rmap -> refcount based
> > on i_metatype.
>
> Ok, can we union the i_projid field (both in memory and in the
> on-disk structure) so that dual use of the field is well documented
> by the code?

Sounds good to me. Does

union {
xfs_prid_t i_projid;
uint32_t i_metagroup;
};

sound ok?

--D

> -Dave.
> --
> Dave Chinner
> david@fromorbit.com