XArray: Prevent node leaks in xas_alloc()

In the following situation, we can leak nodes:

do {
	xas_split_alloc();
	xas_lock();
	/* Discover that xas_split() does not need to be called */
	xas_store();
	xas_unlock();
} while (xas_nomem());

The xas_store() is expecting to be using a node allocated by xas_alloc(),
but will use a node allocated by xas_split_alloc() instead.  That
will cause us to leak the remaining nodes which are chained through
node->parent.  Fix this by only popping the top node off the xa_alloc
list instead of removing all the nodes.

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

diff --git a/lib/xarray.c b/lib/xarray.c
index 32d4bac8c94ca13e11f350c6bcfcacc2040d0359..2da34b84ac46623153983a889420774c292f49d7 100644 (file)
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -366,7 +366,7 @@ static void *xas_alloc(struct xa_state *xas, unsigned int shift)
                return NULL;
 
        if (node) {
-               xas->xa_alloc = NULL;
+               xas->xa_alloc = rcu_dereference_raw(node->parent);
        } else {
                gfp_t gfp = GFP_NOWAIT | __GFP_NOWARN;