Re: [Patch v2] doc/RCU/listRCU: refine example code for eliminating stale data

[Boqun Feng <boqun.feng@gmail.com>]

On Tue, Feb 18, 2025 at 12:50:47AM +0000, Wei Yang wrote:
> This patch adjust the example code with following two purpose:
> 
>   * reduce the confusion on not releasing e->lock
>   * emphasize e is valid and not stale with e->lock held
> 
> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
> CC: Boqun Feng <boqun.feng@gmail.com>
> CC: Alan Huang <mmpgouride@gmail.com>
> 

Alan, could you take a look and if all looks reasonable to you, maybe a
Reviewed-by or Acked-by? Thanks!

Regards,
Boqun

> ---
> v2:
>   * add the missing parameter *key
>   * make function return struct audit_entry
> ---
>  Documentation/RCU/listRCU.rst | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/RCU/listRCU.rst b/Documentation/RCU/listRCU.rst
> index ed5c9d8c9afe..d8bb98623c12 100644
> --- a/Documentation/RCU/listRCU.rst
> +++ b/Documentation/RCU/listRCU.rst
> @@ -334,7 +334,7 @@ If the system-call audit module were to ever need to reject stale data, one way
>  to accomplish this would be to add a ``deleted`` flag and a ``lock`` spinlock to the
>  ``audit_entry`` structure, and modify audit_filter_task() as follows::
>  
> -	static enum audit_state audit_filter_task(struct task_struct *tsk)
> +	static struct audit_entry *audit_filter_task(struct task_struct *tsk, char **key)
>  	{
>  		struct audit_entry *e;
>  		enum audit_state   state;
> @@ -346,16 +346,18 @@ to accomplish this would be to add a ``deleted`` flag and a ``lock`` spinlock to
>  				if (e->deleted) {
>  					spin_unlock(&e->lock);
>  					rcu_read_unlock();
> -					return AUDIT_BUILD_CONTEXT;
> +					return NULL;
>  				}
>  				rcu_read_unlock();
>  				if (state == AUDIT_STATE_RECORD)
>  					*key = kstrdup(e->rule.filterkey, GFP_ATOMIC);
> -				return state;
> +				/* As long as e->lock is held, e is valid and
> +				 * its value is not stale */
> +				return e;
>  			}
>  		}
>  		rcu_read_unlock();
> -		return AUDIT_BUILD_CONTEXT;
> +		return NULL;
>  	}
>  
>  The ``audit_del_rule()`` function would need to set the ``deleted`` flag under the
> -- 
> 2.34.1
> 
>