Re: [linux-next:master 6618/6917] kernel/sched/psi.c:1230:13: sparse: error: incompatible types in comparison expression (different address spaces)

["Paul E. McKenney" <paulmck@linux.ibm.com>]

On Tue, Feb 12, 2019 at 08:25:18AM -0800, Matthew Wilcox wrote:
> On Tue, Feb 12, 2019 at 07:56:10AM -0800, Paul E. McKenney wrote:
> > On Mon, Feb 11, 2019 at 05:36:06PM -0800, Matthew Wilcox wrote:
> > > radix_tree_iter_resume is, happily, gone from my xarray-conv tree.
> > > __radix_tree_lookup, __radix_tree_replace, radix_tree_iter_replace and
> > > radix_tree_iter_init are still present, but hopefully not for too much
> > > longer.  For example, __radix_tree_replace() is (now) called only from
> > > idr_replace(), and there are only 12 remaining callers of idr_replace().
> > 
> > Will this reduce the number of uses of rcu_dereference_raw()?  Or do they
> > simply migrate into Xarray?
> 
> Unlike the radix tree (which let you do whatever awful locking scheme you
> wanted), the XArray requires that you use the spinlock embedded in the
> root of the data structure to protect against simultaneous modification.
> So all dereferences within the XArray code look like this:
> 
> (if either under lock, or rcu lock held):
>         return rcu_dereference_check(node->slots[offset],
>                                                 lockdep_is_held(&xa->xa_lock));
> 
> (if we know the lock is held):
>         return rcu_dereference_protected(node->slots[offset],
>                                                 lockdep_is_held(&xa->xa_lock));
> 
> The XArray API doesn't expose slot pointers to its clients.  It hides them
> inside the xa_state's pointer to the current xa_node.

Nice!!!

							Thanx, Paul