XArray: Fix xa_reserve for 2-byte aligned entries

If we reserve index 0, the next entry to be stored there might be 2-byte
aligned.  That means we have to create the root xa_node at the time of
reserving the initial entry.

Signed-off-by: Matthew Wilcox <willy@infradead.org>

1 files changed, 5 insertions, 3 deletions

diff --git a/lib/xarray.c b/lib/xarray.c
index 2cc3798672f7..6be3acbb861f 100644
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -767,10 +767,12 @@ void *xas_store(struct xa_state *xas, void *entry)
         void *first, *next;
         bool value = xa_is_value(entry);
 
-        if (entry)
-                first = xas_create(xas, !xa_is_node(entry));
-        else
+        if (entry) {
+                bool allow_root = !xa_is_node(entry) && !xa_is_zero(entry);
+                first = xas_create(xas, allow_root);
+        } else {
                 first = xas_load(xas);
+        }
 
         if (xas_invalid(xas))
                 return first;