XArray: Fix xa_for_each with a single element at 0

The following sequence of calls would result in an infinite loop in
xa_find_after():

	xa_store(xa, 0, x, GFP_KERNEL);
	index = 0;
	xa_for_each(xa, entry, index, ULONG_MAX, XA_PRESENT) { }

xa_find_after() was confusing the situation where we found no entry in
the tree with finding a multiorder entry, so it would look for the
successor entry forever.  Just check for this case explicitly.  Includes
a few new checks in the test suite to be sure this doesn't reappear.

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

2 files changed, 31 insertions, 1 deletions

diff --git a/lib/test_xarray.c b/lib/test_xarray.c
index aa47754150ce..126127658b49 100644
--- a/lib/test_xarray.c
+++ b/lib/test_xarray.c
@@ -702,7 +702,7 @@ static noinline void check_multi_find_2(struct xarray *xa)
         }
 }
 
-static noinline void check_find(struct xarray *xa)
+static noinline void check_find_1(struct xarray *xa)
 {
         unsigned long i, j, k;
 
@@ -748,6 +748,34 @@ static noinline void check_find(struct xarray *xa)
                 XA_BUG_ON(xa, xa_get_mark(xa, i, XA_MARK_0));
         }
         XA_BUG_ON(xa, !xa_empty(xa));
+}
+
+static noinline void check_find_2(struct xarray *xa)
+{
+        void *entry;
+        unsigned long i, j, index = 0;
+
+        xa_for_each(xa, entry, index, ULONG_MAX, XA_PRESENT) {
+                XA_BUG_ON(xa, true);
+        }
+
+        for (i = 0; i < 1024; i++) {
+                xa_store_index(xa, index, GFP_KERNEL);
+                j = 0;
+                index = 0;
+                xa_for_each(xa, entry, index, ULONG_MAX, XA_PRESENT) {
+                        XA_BUG_ON(xa, xa_mk_value(index) != entry);
+                        XA_BUG_ON(xa, index != j++);
+                }
+        }
+
+        xa_destroy(xa);
+}
+
+static noinline void check_find(struct xarray *xa)
+{
+        check_find_1(xa);
+        check_find_2(xa);
         check_multi_find(xa);
         check_multi_find_2(xa);
 }
diff --git a/lib/xarray.c b/lib/xarray.c
index 8b176f009c08..c991ff4523ef 100644
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -1829,6 +1829,8 @@ void *xa_find_after(struct xarray *xa, unsigned long *indexp,
                         entry = xas_find_marked(&xas, max, filter);
                 else
                         entry = xas_find(&xas, max);
+                if (xas.xa_node == XAS_BOUNDS)
+                        break;
                 if (xas.xa_shift) {
                         if (xas.xa_index & ((1UL << xas.xa_shift) - 1))
                                 continue;