Re: [PATCH tip/core/rcu 07/12] rcu: No ordering for rcu_assign_pointer() of NULL

[Peter Zijlstra]

On Wed, Jun 15, 2016 at 02:46:08PM -0700, Paul E. McKenney wrote:
> This commit does a compile-time check for rcu_assign_pointer() of NULL,
> and uses WRITE_ONCE() rather than smp_store_release() in that case.
> 
> Reported-by: Christoph Hellwig <hch@xxxxxxxxxxxxx>
> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> ---
>  include/linux/rcupdate.h | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index c61b6b9506e7..9be61e47badc 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -650,7 +650,16 @@ static inline void rcu_preempt_sleep_check(void)
>   * please be careful when making changes to rcu_assign_pointer() and the
>   * other macros that it invokes.
>   */
> -#define rcu_assign_pointer(p, v) smp_store_release(&p, RCU_INITIALIZER(v))
> +#define rcu_assign_pointer(p, v) \
> +({ \
> +	uintptr_t _r_a_p__v = (uintptr_t)(v); \
> +	\
> +	if (__builtin_constant_p(v) && (_r_a_p__v) == (uintptr_t)NULL) \
> +		WRITE_ONCE((p), (typeof(p))(_r_a_p__v)); \
> +	else \
> +		smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \
> +	_r_a_p__v; \
> +})

Can we pretty please right align the '\'s ?

Also, didn't we used to do this and then reverted it again for some
obscure reason?