drivers/hwspinlock: fix race between radix tree insertion and lookup

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@linux.intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ohad Ben-Cohen <ohad@wizery.com>
Cc: Konstantin Khlebnikov <khlebnikov@openvz.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/hwspinlock/hwspinlock_core.c b/drivers/hwspinlock/hwspinlock_core.c
index 52f708b..d50c701 100644 (file)
--- 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;