[tip: core/rcu] rculist: Add brackets around cond argument in __list_check_rcu macro

[tip-bot2 for Amol Grover]

The following commit has been merged into the core/rcu branch of tip:

Commit-ID:     4dfd5cd83dc4458049c7f6eb9c4f361acc4239ea
Gitweb:        https://git.kernel.org/tip/4dfd5cd83dc4458049c7f6eb9c4f361acc4239ea
Author:        Amol Grover <frextrite@xxxxxxxxx>
AuthorDate:    Sat, 18 Jan 2020 22:24:18 +05:30
Committer:     Paul E. McKenney <paulmck@xxxxxxxxxx>
CommitterDate: Thu, 20 Feb 2020 15:58:23 -08:00

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@xxxxxxxxx>
Acked-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
 include/linux/rculist.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index 9f313e4..8214cdc 100644
--- 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); })