lib/radix-tree.c: swapoff tmpfs radix_tree: remember to rcu_read_unlock

Running fsx on tmpfs with concurrent memhog-swapoff-swapon, lots of

  BUG: sleeping function called from invalid context at kernel/fork.c:606
  in_atomic(): 0, irqs_disabled(): 0, pid: 1394, name: swapoff
  1 lock held by swapoff/1394:
   #0:  (rcu_read_lock){.+.+.+}, at: [<ffffffff812520a1>] radix_tree_locate_item+0x1f/0x2b6

followed by

  ================================================
  [ BUG: lock held when returning to user space! ]
  3.14.0-rc1 #3 Not tainted
  ------------------------------------------------
  swapoff/1394 is leaving the kernel with locks still held!
  1 lock held by swapoff/1394:
   #0:  (rcu_read_lock){.+.+.+}, at: [<ffffffff812520a1>] radix_tree_locate_item+0x1f/0x2b6

after which the system recovered nicely.

Whoops, I long ago forgot the rcu_read_unlock() on one unlikely branch.

Fixes e504f3fdd63d ("tmpfs radix_tree: locate_item to speed up swapoff")

Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 1 deletions

diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 7811ed3b4e70..bd4a8dfdf0b8 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -1253,8 +1253,10 @@ unsigned long radix_tree_locate_item(struct radix_tree_root *root, void *item)
 
                 node = indirect_to_ptr(node);
                 max_index = radix_tree_maxindex(node->height);
-                if (cur_index > max_index)
+                if (cur_index > max_index) {
+                        rcu_read_unlock();
                         break;
+                }
 
                 cur_index = __locate(node, item, cur_index, &found_index);
                 rcu_read_unlock();