Re: [RFC PATCH 12/21] list: Poison ->next pointer for non-RCU deletion of 'hlist_nulls_node'

[Paul E. McKenney]

On Tue, Mar 24, 2020 at 03:36:34PM +0000, Will Deacon wrote:
> hlist_nulls_del() is used for non-RCU deletion of an 'hlist_nulls_node'
> and so we can safely poison the ->next pointer without having to worry
> about concurrent readers, just like we do for other non-RCU list
> deletion primitives
> 
> Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Signed-off-by: Will Deacon <will@xxxxxxxxxx>

Agreed, any code having difficulty with this change should use instead
hlist_nulls_del_rcu().

Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxx>

> ---
>  include/linux/list_nulls.h | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/include/linux/list_nulls.h b/include/linux/list_nulls.h
> index fd154ceb5b0d..48f33ae16381 100644
> --- a/include/linux/list_nulls.h
> +++ b/include/linux/list_nulls.h
> @@ -99,6 +99,7 @@ static inline void __hlist_nulls_del(struct hlist_nulls_node *n)
>  static inline void hlist_nulls_del(struct hlist_nulls_node *n)
>  {
>  	__hlist_nulls_del(n);
> +	n->next = LIST_POISON1;
>  	n->pprev = LIST_POISON2;
>  }
>  
> -- 
> 2.20.1
>