Re: XFS reclaim lock order bug

Dave Chinner
2010-11-25T10:30:38Z

On Thu, Nov 25, 2010 at 08:28:17AM +0100, Peter Zijlstra wrote:
> On Thu, 2010-11-25 at 18:08 +1100, Nick Piggin wrote:
> > > +static struct lock_class_key xfs_dead_inode;
> > > +
> > > STATIC void
> > > xfs_fs_evict_inode(
> > > struct inode *inode)
> > > @@ -1118,6 +1120,8 @@ xfs_fs_evict_inode(
> > > */
> > > ASSERT(!rwsem_is_locked(&ip->i_iolock.mr_lock));
> > > mrlock_init(&ip->i_iolock, MRLOCK_BARRIER, "xfsio", ip->i_ino);
> > > + lockdep_set_class_and_name(&ip->i_iolock->mr_lock, &xfs_dead_inode,
> > > + "xfd_dead_inode");
> > >
> > > xfs_inactive(ip);
> > > }
> >
> > With this change, I assume the mrlock_init can go? (it would be nice
> > to have a wrapper to allocate the class by itself)
>
>
> mrlock_init() does allocate a class (well rwsem_init, really), but sets
> the name to a stringified version of the lock argument.
>
> The lockdep_set_class*() interface is only guaranteed to work on a
> freshly initialized lock structure -- which in this case is a bit of a
> waste, but for debugging purposes would allow setting a clearer name.
>
> Alternatively, you can write the code like:
>
> xfs_inode_t dead_ip = XFS_I(inode);
>
> mrlock_init(&dead_ip->i_iolock, ...);
>
> In which case its also obvious, as that would result in:
>
> (&(&dead_ip->i_iolock)->mr_lock)
>
> as opposed to:
>
> (&(&ip->i_iolock)->mr_lock)

Ok, that's a handy trick to know. I'll try and sort this out
tomorrow and make use of this trick to help identify the different
lock classes.

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com