Re: rcu: fix hlist_bl_set_first_rcu annotation

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Wed, Jan 30, 2013 at 07:07:57PM +0000, Steven Whitehouse wrote:
> 
> Abhi noticed that we were getting a complaint from the RCU subsystem
> about access of an RCU protected list under the write side bit lock.
> This patch adds additional annotation to check both the RCU read
> lock and the write side bit lock before printing a message.
> 
> Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
> Reported-by: Abhijith Das <adas@redhat.com>
> Tested-by: Abhijith Das <adas@redhat.com>

Looks plausible to me on first glance, copying Nick Piggin and Christoph
Hellwig.  If they have no objections, I will queue this.

							Thanx, Paul

> diff --git a/include/linux/list_bl.h b/include/linux/list_bl.h
> index 31f9d75..2eb8855 100644
> --- a/include/linux/list_bl.h
> +++ b/include/linux/list_bl.h
> @@ -125,6 +125,11 @@ static inline void hlist_bl_unlock(struct hlist_bl_head *b)
>  	__bit_spin_unlock(0, (unsigned long *)b);
>  }
> 
> +static inline bool hlist_bl_is_locked(struct hlist_bl_head *b)
> +{
> +	return bit_spin_is_locked(0, (unsigned long *)b);
> +}
> +
>  /**
>   * hlist_bl_for_each_entry	- iterate over list of given type
>   * @tpos:	the type * to use as a loop cursor.
> diff --git a/include/linux/rculist_bl.h b/include/linux/rculist_bl.h
> index cf1244f..4f216c5 100644
> --- a/include/linux/rculist_bl.h
> +++ b/include/linux/rculist_bl.h
> @@ -20,7 +20,7 @@ static inline void hlist_bl_set_first_rcu(struct hlist_bl_head *h,
>  static inline struct hlist_bl_node *hlist_bl_first_rcu(struct hlist_bl_head *h)
>  {
>  	return (struct hlist_bl_node *)
> -		((unsigned long)rcu_dereference(h->first) & ~LIST_BL_LOCKMASK);
> +		((unsigned long)rcu_dereference_check(h->first, hlist_bl_is_locked(h)) & ~LIST_BL_LOCKMASK);
>  }
> 
>  /**
> 
>