linux-kernel - Re: [PATCH] rculist: move hlist_del_init

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Message-ID: <20160116005001.GI3818@linux.vnet.ibm.com>
Date:	Fri, 15 Jan 2016 16:50:01 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Geliang Tang <geliangtang@....com>
Cc:	Josh Triplett <josh@...htriplett.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rculist: move hlist_del_init_rcu to a proper place

On Tue, Jan 12, 2016 at 11:08:30PM +0800, Geliang Tang wrote:
> hlist_del_init_rcu() should not behind list_del_rcu(), should behind
> hlist_del_rcu().
> 
> Signed-off-by: Geliang Tang <geliangtang@....com>

Can't say I am all that excited by this one.  Anyone on CC willing to
speak up for it?

							Thanx, Paul

> ---
>  include/linux/rculist.h | 56 ++++++++++++++++++++++++-------------------------
>  1 file changed, 28 insertions(+), 28 deletions(-)
> 
> diff --git a/include/linux/rculist.h b/include/linux/rculist.h
> index 14ec165..99bed04 100644
> --- a/include/linux/rculist.h
> +++ b/include/linux/rculist.h
> @@ -133,34 +133,6 @@ static inline void list_del_rcu(struct list_head *entry)
>  }
> 
>  /**
> - * hlist_del_init_rcu - deletes entry from hash list with re-initialization
> - * @n: the element to delete from the hash list.
> - *
> - * Note: list_unhashed() on the node return true after this. It is
> - * useful for RCU based read lockfree traversal if the writer side
> - * must know if the list entry is still hashed or already unhashed.
> - *
> - * In particular, it means that we can not poison the forward pointers
> - * that may still be used for walking the hash list and we can only
> - * zero the pprev pointer so list_unhashed() will return true after
> - * this.
> - *
> - * The caller must take whatever precautions are necessary (such as
> - * holding appropriate locks) to avoid racing with another
> - * list-mutation primitive, such as hlist_add_head_rcu() or
> - * hlist_del_rcu(), running on this same list.  However, it is
> - * perfectly legal to run concurrently with the _rcu list-traversal
> - * primitives, such as hlist_for_each_entry_rcu().
> - */
> -static inline void hlist_del_init_rcu(struct hlist_node *n)
> -{
> -	if (!hlist_unhashed(n)) {
> -		__hlist_del(n);
> -		n->pprev = NULL;
> -	}
> -}
> -
> -/**
>   * list_replace_rcu - replace old entry by new one
>   * @old : the element to be replaced
>   * @new : the new element to insert
> @@ -409,6 +381,34 @@ static inline void hlist_del_rcu(struct hlist_node *n)
>  }
> 
>  /**
> + * hlist_del_init_rcu - deletes entry from hash list with re-initialization
> + * @n: the element to delete from the hash list.
> + *
> + * Note: list_unhashed() on the node return true after this. It is
> + * useful for RCU based read lockfree traversal if the writer side
> + * must know if the list entry is still hashed or already unhashed.
> + *
> + * In particular, it means that we can not poison the forward pointers
> + * that may still be used for walking the hash list and we can only
> + * zero the pprev pointer so list_unhashed() will return true after
> + * this.
> + *
> + * The caller must take whatever precautions are necessary (such as
> + * holding appropriate locks) to avoid racing with another
> + * list-mutation primitive, such as hlist_add_head_rcu() or
> + * hlist_del_rcu(), running on this same list.  However, it is
> + * perfectly legal to run concurrently with the _rcu list-traversal
> + * primitives, such as hlist_for_each_entry_rcu().
> + */
> +static inline void hlist_del_init_rcu(struct hlist_node *n)
> +{
> +	if (!hlist_unhashed(n)) {
> +		__hlist_del(n);
> +		n->pprev = NULL;
> +	}
> +}
> +
> +/**
>   * hlist_replace_rcu - replace old entry by new one
>   * @old : the element to be replaced
>   * @new : the new element to insert
> -- 
> 2.5.0
> 
>