rculist: Add brackets around cond argument in __list_check_rcu macro

Passing a complex lockdep condition to __list_check_rcu results
in false positive lockdep splat due to incorrect expression
evaluation.

For example, a lockdep check condition `cond1 || cond2` is
evaluated as `!cond1 || cond2 && !rcu_read_lock_any_held()`
which, according to operator precedence, evaluates to
`!cond1 || (cond2 && !rcu_read_lock_any_held())`.
This would result in a lockdep splat when cond1 is false
and cond2 is true which is logically incorrect.

Signed-off-by: Amol Grover <frextrite@gmail.com>
Acked-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index 9f313e4..8214cdc 100644 (file)
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -60,9 +60,9 @@ static inline void INIT_LIST_HEAD_RCU(struct list_head *list)
 #define __list_check_rcu(dummy, cond, extra...)                                \
        ({                                                              \
        check_arg_count_one(extra);                                     \
-       RCU_LOCKDEP_WARN(!cond && !rcu_read_lock_any_held(),            \
+       RCU_LOCKDEP_WARN(!(cond) && !rcu_read_lock_any_held(),          \
                         "RCU-list traversed in non-reader section!");  \
-        })
+       })
 #else
 #define __list_check_rcu(dummy, cond, extra...)                                \
        ({ check_arg_count_one(extra); })