From: Matthew Wilcox <willy@infradead.org>
Date: Thu, 21 Feb 2019 22:54:44 +0000 (-0500)
Subject: XArray: Fix xa_reserve for 2-byte aligned entries
X-Git-Tag: v5.1-rc1~58^2
X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=4a5c8d898948d1ac876522cdd62f07a78104bfe9;p=linux-2.6-block.git

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>
---

diff --git a/lib/test_xarray.c b/lib/test_xarray.c
index bc202d468a6b..5d4bad8bd96a 100644
--- 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
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;