Re: RCU: how to suppress warnings from rcu_assign_pointer?

[Eric Dumazet <eric.dumazet@gmail.com>]

Le vendredi 29 juillet 2011 à 10:50 -0700, Stephen Hemminger a écrit :
> Gcc now generates warnings from rcu_assign_pointer when passed the
> address of something for example:
> 	rcu_assign_pointer(dev_queue->qdisc, &noop_qdisc);
> This warning is harmless and should be surpressed but there maybe
> other cases where we want that Gcc warning.
> 
> I tried various combinations of in rcu_assign_pointer macro
>   #pragma GCC diagnostic push
>   #pragma GCC diagnostic ignored "-Wlogical-op"
>   ...
>   #pragma GCC diagnostic pop
> but macro's and pragma's don't nest with the correct scope for
> this.
> 
> Maybe some one with more Gcc foo and time to waste could take
> a crack at it.

I would just remove the test from rcu_assign_pointer().

We now have RCU_INIT_POINTER() for places we dont want/afford the
smp_wmb()


diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 8f4f881..f372e88 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -365,9 +365,7 @@ extern int rcu_my_thread_group_empty(void);
 	})
 #define __rcu_assign_pointer(p, v, space) \
 	({ \
-		if (!__builtin_constant_p(v) || \
-		    ((v) != NULL)) \
-			smp_wmb(); \
+		smp_wmb(); \
 		(p) = (typeof(*v) __force space *)(v); \
 	})