Re: [PATCH] md: do not use ++ in rcu_dereference() argument

Arnd Bergmann
2010-09-06T20:10:55Z

On Sunday 05 September 2010 20:32:18 Kulikov Vasiliy wrote:
> From: Vasiliy Kulikov <segooon@gmail.com>
>
> rcu_dereference() is macro, so it might use its argument twice.
> Argument must not has side effects.
>
> It was found by compiler warning:
> drivers/md/raid1.c: In function ‘read_balance’:
> drivers/md/raid1.c:445: warning: operation on ‘new_disk’ may be undefined

I think the rcu_dereference macro should really not evaluate its argument
twice, and I don't see where it does.
As a general rule, we try to write macros in Linux such that they behave
like functions and don't have surprising side-effects.

Which kernel and gcc version do you see the warning with?

Arnd