[PATCH 4.4 115/137] drivers/hwspinlock: fix race between radix tree insertion and lookup

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

------------------

From: Matthew Wilcox <redacted>

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 <redacted>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ohad Ben-Cohen <redacted>
Cc: Konstantin Khlebnikov <redacted>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/hwspinlock/hwspinlock_core.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/drivers/hwspinlock/hwspinlock_core.c
+++ b/drivers/hwspinlock/hwspinlock_core.c

@@ -313,6 +313,10 @@ int of_hwspin_lock_get_id(struct device_
 		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;