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 <[email protected]>
majek · Feb 21, 2019 · 4a5c8d8 · 4a5c8d8
1 parent 2fbe967
commit 4a5c8d8
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Showing 2 changed files with 15 additions and 3 deletions.
diff --git a/lib/test_xarray.c b/lib/test_xarray.c
@@ -1355,6 +1355,10 @@ static void check_align_1(struct xarray *xa, char *name)
 	xa_destroy(xa);
 }
 
+/*
+ * We should always be able to store without allocating memory after
+ * reserving a slot.
+ */
 static void check_align_2(struct xarray *xa, char *name)
 {
 	int i;
@@ -1366,6 +1370,12 @@ static void check_align_2(struct xarray *xa, char *name)
 		xa_erase(xa, 0);
 	}
 
+	for (i = 0; i < 8; i++) {
+		XA_BUG_ON(xa, xa_reserve(xa, 0, GFP_KERNEL) != 0);
+		XA_BUG_ON(xa, xa_store(xa, 0, name + i, 0) != NULL);
+		xa_erase(xa, 0);
+	}
+
 	XA_BUG_ON(xa, !xa_empty(xa));
 }
 

diff --git 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;