Re: [PATCH v3] Fixes: 07928d9bfc81 ("padata: Remove broken queue flushing")

[Daniel Jordan]

Hi,

On Sat, Oct 07, 2023 at 11:52:33AM +0800, Wang Jinchao wrote:
> Signed-off-by: Wang Jinchao <wangjinchao@xxxxxxxxxxx>

The Fixes: tag should be near your Signed-off-by:, and the subject of
the patch should be something descriptive like

    padata: Fix refcnt handling in padata_free_shell()

Here's some documentation about this:

    https://docs.kernel.org/process/5.Posting.html#patch-formatting-and-changelogs

> Acked-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
> ---
> V3: 
>     Include Daniel's ack
>
> V2: https://lore.kernel.org/all/ZRTLHY5A+VqIKhA2@fedora/
>     To satisfy Sparse, use rcu_dereference_protected.
>     Reported-by: kernel test robot <lkp@xxxxxxxxx>
>     Closes: https://lore.kernel.org/oe-kbuild-all/202309270829.xHgTOMKw-lkp@xxxxxxxxx/

These two tags can also go near your SoB.

> V1: https://lore.kernel.org/all/ZRE4XvOOhz4HSOgR@fedora/
> 
>  kernel/padata.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/padata.c b/kernel/padata.c
> index 222d60195de6..79d04a97ded6 100644
> --- a/kernel/padata.c
> +++ b/kernel/padata.c
> @@ -1102,12 +1102,16 @@ EXPORT_SYMBOL(padata_alloc_shell);
>   */
>  void padata_free_shell(struct padata_shell *ps)
>  {
> +	struct parallel_data *pd;
> +
>  	if (!ps)
>  		return;
>  
>  	mutex_lock(&ps->pinst->lock);
>  	list_del(&ps->list);
> -	padata_free_pd(rcu_dereference_protected(ps->pd, 1));
> +	pd = rcu_dereference_protected(ps->pd, 1);
> +	if (refcount_dec_and_test(&pd->refcnt))
> +		padata_free_pd(rcu_dereference_protected(ps->pd, 1));

As Herbert points out, this version changes the code by
rcu-dereferencing pd twice.  Usually previous acks are dropped when
introducing new changes, but you can have it back by only
rcu-dereferencing once and addressing the other comments above.

>  	mutex_unlock(&ps->pinst->lock);
>  
>  	kfree(ps);
> -- 
> 2.40.0
>