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.

Amol Grover committed 6 years ago

Commit 4dfd5cd1 parent aa24f931 file · +2 −2Browse files

Unified · Split

include/linux/rculist.h+2−2

@@ -60,9 +60,9 @@ static inline void INIT_LIST_HEAD_RCU(struct list_head *list) · 59 unmodified lines
60	60	#define __list_check_rcu(dummy, cond, extra...) \
61	61	({ \
62	62	check_arg_count_one(extra); \
63		− RCU_LOCKDEP_WARN(!cond && !rcu_read_lock_any_held(), \
	63	+ RCU_LOCKDEP_WARN(!(cond) && !rcu_read_lock_any_held(), \
64	64	"RCU-list traversed in non-reader section!"); \
65		− })
	65	+ })
66	66	#else
67	67	#define __list_check_rcu(dummy, cond, extra...) \
68	68	({ check_arg_count_one(extra); })