Re: [RFC PATCH 07/21] Revert "list: Use WRITE_ONCE() when adding to lists and hlists"

[Paul E. McKenney]

On Tue, Mar 24, 2020 at 03:36:29PM +0000, Will Deacon wrote:
> This reverts commit 1c97be677f72b3c338312aecd36d8fff20322f32.
> 
> There is no need to use WRITE_ONCE() for the non-RCU list and hlist
> implementations.
> 
> Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Signed-off-by: Will Deacon <will@xxxxxxxxxx>

Which means that the lockless uses of hlist_empty() will also need
attention, correct?

							Thanx, Paul

> ---
>  include/linux/list.h | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/list.h b/include/linux/list.h
> index ec1f780d1449..c7331c259792 100644
> --- a/include/linux/list.h
> +++ b/include/linux/list.h
> @@ -70,7 +70,7 @@ static inline void __list_add(struct list_head *new,
>  	next->prev = new;
>  	new->next = next;
>  	new->prev = prev;
> -	WRITE_ONCE(prev->next, new);
> +	prev->next = new;
>  }
>  
>  /**
> @@ -843,7 +843,7 @@ static inline void hlist_add_head(struct hlist_node *n, struct hlist_head *h)
>  	n->next = first;
>  	if (first)
>  		first->pprev = &n->next;
> -	WRITE_ONCE(h->first, n);
> +	h->first = n;
>  	n->pprev = &h->first;
>  }
>  
> @@ -858,7 +858,7 @@ static inline void hlist_add_before(struct hlist_node *n,
>  	n->pprev = next->pprev;
>  	n->next = next;
>  	next->pprev = &n->next;
> -	WRITE_ONCE(*(n->pprev), n);
> +	*(n->pprev) = n;
>  }
>  
>  /**
> -- 
> 2.20.1
>