Re: [PATCH RFC 5/5] rcuwait: Replace rcu_assign_pointer() with WRITE_ONCE

From: Peter Zijlstra
Date: Thu Feb 21 2019 - 04:20:54 EST


On Thu, Feb 21, 2019 at 12:49:42AM -0500, Joel Fernandes (Google) wrote:
> This suppresses a sparse error generated due to the recently added
> rcu_assign_pointer sparse check below. It seems WRITE_ONCE should be
> sufficient here.
>
> >> kernel//locking/percpu-rwsem.c:162:9: sparse: error: incompatible
> types in comparison expression (different address spaces)
>
> Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
> ---
> include/linux/rcuwait.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/rcuwait.h b/include/linux/rcuwait.h
> index 90bfa3279a01..9e5b4760e6c2 100644
> --- a/include/linux/rcuwait.h
> +++ b/include/linux/rcuwait.h
> @@ -44,7 +44,7 @@ extern void rcuwait_wake_up(struct rcuwait *w);
> */ \
> WARN_ON(current->exit_state); \
> \
> - rcu_assign_pointer((w)->task, current); \
> + WRITE_ONCE((w)->task, current); \
> for (;;) { \
> /* \
> * Implicit barrier (A) pairs with (B) in \

Distinct lack of justification for loosing the RELEASE again.