[PATCH 5.3 004/135] XArray: Fix xas_next() with a single entry at 0

Greg Kroah-Hartman
2019-12-03T22:40:58Z

From: Matthew Wilcox (Oracle) <willy@infradead.org>

[ Upstream commit 91abab83839aa2eba073e4a63c729832fdb27ea1 ]

If there is only a single entry at 0, the first time we call xas_next(),
we return the entry. Unfortunately, all subsequent times we call
xas_next(), we also return the entry at 0 instead of noticing that the
xa_index is now greater than zero. This broke find_get_pages_contig().

Fixes: 64d3e9a9e0cc ("xarray: Step through an XArray")
Reported-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
lib/test_xarray.c | 24 ++++++++++++++++++++++++
lib/xarray.c | 4 ++++
2 files changed, 28 insertions(+)

diff --git a/lib/test_xarray.c b/lib/test_xarray.c
index 9d631a7b6a705..7df4f7f395bf2 100644
--- a/lib/test_xarray.c
+++ b/lib/test_xarray.c
@@ -1110,6 +1110,28 @@ static noinline void check_find_entry(struct xarray *xa)
XA_BUG_ON(xa, !xa_empty(xa));
}

+static noinline void check_move_tiny(struct xarray *xa)
+{
+ XA_STATE(xas, xa, 0);
+
+ XA_BUG_ON(xa, !xa_empty(xa));
+ rcu_read_lock();
+ XA_BUG_ON(xa, xas_next(&xas) != NULL);
+ XA_BUG_ON(xa, xas_next(&xas) != NULL);
+ rcu_read_unlock();
+ xa_store_index(xa, 0, GFP_KERNEL);
+ rcu_read_lock();
+ xas_set(&xas, 0);
+ XA_BUG_ON(xa, xas_next(&xas) != xa_mk_index(0));
+ XA_BUG_ON(xa, xas_next(&xas) != NULL);
+ xas_set(&xas, 0);
+ XA_BUG_ON(xa, xas_prev(&xas) != xa_mk_index(0));
+ XA_BUG_ON(xa, xas_prev(&xas) != NULL);
+ rcu_read_unlock();
+ xa_erase_index(xa, 0);
+ XA_BUG_ON(xa, !xa_empty(xa));
+}
+
static noinline void check_move_small(struct xarray *xa, unsigned long idx)
{
XA_STATE(xas, xa, 0);
@@ -1217,6 +1239,8 @@ static noinline void check_move(struct xarray *xa)

xa_destroy(xa);

+ check_move_tiny(xa);
+
for (i = 0; i < 16; i++)
check_move_small(xa, 1UL << i);

diff --git a/lib/xarray.c b/lib/xarray.c
index 446b956c91888..1237c213f52bc 100644
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -994,6 +994,8 @@ void *__xas_prev(struct xa_state *xas)

if (!xas_frozen(xas->xa_node))
xas->xa_index--;
+ if (!xas->xa_node)
+ return set_bounds(xas);
if (xas_not_node(xas->xa_node))
return xas_load(xas);

@@ -1031,6 +1033,8 @@ void *__xas_next(struct xa_state *xas)

if (!xas_frozen(xas->xa_node))
xas->xa_index++;
+ if (!xas->xa_node)
+ return set_bounds(xas);
if (xas_not_node(xas->xa_node))
return xas_load(xas);

--
2.20.1