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

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

On Thu, Feb 20, 2025 at 12:40:20AM +0800, Alan Huang wrote:
> On Feb 18, 2025, at 08:50, Wei Yang <richard.weiyang@gmail.com> 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>
> > 
> > ---
> > 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
> > 
> 
> I think it’s good enough to illustrate the intention here:
> 
> Reviewed-by: Alan Huang <mmpgouride@gmail.com>
> 

Queued for further tests and reviews, thanks you both!

> Boqun, there is an unreviewed doc patch[1] that fixes the section
> 
>  “Using RCU hlist_nulls to protect list and objects”
> 
> [1] https://lore.kernel.org/rcu/20240326124431.77430-1-mmpgouride@gmail.com/
> 
> : )
> 

Will take a look later.

Regards,
Boqun

> 
> 
>