linux-kernel - Re: [PATCH v3 1/6] list: Don't use WRITE_ONCE() in hlist_add

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Message-Id: <20190318153925.GH4102@linux.ibm.com>
Date:   Mon, 18 Mar 2019 08:39:25 -0700
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     Nikos Tsironis <ntsironis@...ikto.com>
Cc:     snitzer@...hat.com, agk@...hat.com, dm-devel@...hat.com,
        mpatocka@...hat.com, hch@...radead.org, iliastsi@...ikto.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/6] list: Don't use WRITE_ONCE() in hlist_add_behind()

On Sun, Mar 17, 2019 at 02:22:53PM +0200, Nikos Tsironis wrote:
> Commit 1c97be677f72b3 ("list: Use WRITE_ONCE() when adding to lists and
> hlists") introduced the use of WRITE_ONCE() to atomically write the list
> head's ->next pointer.
> 
> hlist_add_behind() doesn't touch the hlist head's ->first pointer so
> there is no reason to use WRITE_ONCE() in this case.
> 
> Signed-off-by: Nikos Tsironis <ntsironis@...ikto.com>
> Signed-off-by: Ilias Tsitsimpis <iliastsi@...ikto.com>

Reviewed-by: Paul E. McKenney <paulmck@...ux.ibm.com>

> ---
>  include/linux/list.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/list.h b/include/linux/list.h
> index edb7628e46ed..b68d2a85859b 100644
> --- a/include/linux/list.h
> +++ b/include/linux/list.h
> @@ -743,7 +743,7 @@ static inline void hlist_add_behind(struct hlist_node *n,
>  				    struct hlist_node *prev)
>  {
>  	n->next = prev->next;
> -	WRITE_ONCE(prev->next, n);
> +	prev->next = n;
>  	n->pprev = &prev->next;
>  
>  	if (n->next)
> -- 
> 2.11.0
>