[PATCH net-next 7/7] rcu: prevent RCU_LOCKDEP_WARN() from swallowing the condition

Jakub Kicinski
2020-09-16T18:47:23Z

We run into a unused variable warning in bridge code when
variable is only used inside the condition of
rcu_dereference_protected().

#define mlock_dereference(X, br) \
rcu_dereference_protected(X, lockdep_is_held(&br->multicast_lock))

Since on builds with CONFIG_PROVE_RCU=n rcu_dereference_protected()
compiles to nothing the compiler doesn't see the variable use.

Prevent the warning by adding the condition as dead code.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
--
CC: paulmck@kernel.org
CC: josh@joshtriplett.org
CC: rostedt@goodmis.org
CC: mathieu.desnoyers@efficios.com
CC: joel@joelfernandes.org
CC: jiangshanlai@gmail.com
---
include/linux/rcupdate.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 53f9648cb982..50d45781fa99 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -321,7 +321,7 @@ static inline void rcu_preempt_sleep_check(void) { }

#else /* #ifdef CONFIG_PROVE_RCU */

-#define RCU_LOCKDEP_WARN(c, s) do { } while (0)
+#define RCU_LOCKDEP_WARN(c, s) do { } while (0 && (c))
#define rcu_sleep_check() do { } while (0)

#endif /* #else #ifdef CONFIG_PROVE_RCU */
--
2.26.2