[PATCH 4.2.y-ckt 078/273] drivers/hwspinlock: fix race between radix tree insertion and lookup

[Kamal Mostafa]

4.2.8-ckt5 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Matthew Wilcox <willy at linux.intel.com>

commit c6400ba7e13a41539342f1b6e1f9e78419cb0148 upstream.

of_hwspin_lock_get_id() is protected by the RCU lock, which means that
insertions can occur simultaneously with the lookup.  If the radix tree
transitions from a height of 0, we can see a slot with the indirect_ptr
bit set, which will cause us to at least read random memory, and could
cause other havoc.

Fix this by using the newly introduced radix_tree_iter_retry().

Signed-off-by: Matthew Wilcox <willy at linux.intel.com>
Cc: Hugh Dickins <hughd at google.com>
Cc: Ohad Ben-Cohen <ohad at wizery.com>
Cc: Konstantin Khlebnikov <khlebnikov at openvz.org>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/hwspinlock/hwspinlock_core.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/hwspinlock/hwspinlock_core.c b/drivers/hwspinlock/hwspinlock_core.c
index 52f708b..d50c701 100644
--- a/drivers/hwspinlock/hwspinlock_core.c
+++ b/drivers/hwspinlock/hwspinlock_core.c
@@ -313,6 +313,10 @@ int of_hwspin_lock_get_id(struct device_node *np, int index)
 		hwlock = radix_tree_deref_slot(slot);
 		if (unlikely(!hwlock))
 			continue;
+		if (radix_tree_is_indirect_ptr(hwlock)) {
+			slot = radix_tree_iter_retry(&iter);
+			continue;
+		}
 
 		if (hwlock->bank->dev->of_node == args.np) {
 			ret = 0;
-- 
2.7.0