Re: [PATCH 2/3] soc: qcom: rpmh: Update rpm_msgs offset address and add list_del

[Evan Green <evgreen@chromium.org>]

On Mon, Feb 3, 2020 at 10:14 PM Maulik Shah <mkshah@codeaurora.org> wrote:
>
> rpm_msgs are copied in continuously allocated memory during write_batch.
> Update request pointer to correctly point to designated area for rpm_msgs.
>
> While at this also add missing list_del before freeing rpm_msgs.
>
> Signed-off-by: Maulik Shah <mkshah@codeaurora.org>
> ---
>  drivers/soc/qcom/rpmh.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/soc/qcom/rpmh.c b/drivers/soc/qcom/rpmh.c
> index c3d6f00..04c7805 100644
> --- a/drivers/soc/qcom/rpmh.c
> +++ b/drivers/soc/qcom/rpmh.c
> @@ -65,7 +65,7 @@ struct cache_req {
>  struct batch_cache_req {
>         struct list_head list;
>         int count;
> -       struct rpmh_request rpm_msgs[];
> +       struct rpmh_request *rpm_msgs;
>  };
>
>  static struct rpmh_ctrlr *get_rpmh_ctrlr(const struct device *dev)
> @@ -327,8 +327,10 @@ static void invalidate_batch(struct rpmh_ctrlr *ctrlr)
>         unsigned long flags;
>
>         spin_lock_irqsave(&ctrlr->cache_lock, flags);
> -       list_for_each_entry_safe(req, tmp, &ctrlr->batch_cache, list)
> +       list_for_each_entry_safe(req, tmp, &ctrlr->batch_cache, list) {
> +               list_del(&req->list);
>                 kfree(req);
> +       }
>         INIT_LIST_HEAD(&ctrlr->batch_cache);

Hm, I don't get it. list_for_each_entry_safe ensures you can traverse
the list while freeing it behind you. ctrlr->batch_cache is now a
bogus list, but is re-inited with the lock held. From my reading,
there doesn't seem to be anything wrong with the current code. Can you
elaborate on the bug you found?

>         spin_unlock_irqrestore(&ctrlr->cache_lock, flags);
>  }
> @@ -377,10 +379,11 @@ int rpmh_write_batch(const struct device *dev, enum rpmh_state state,
>                 return -ENOMEM;
>
>         req = ptr;
> +       rpm_msgs = ptr + sizeof(*req);
>         compls = ptr + sizeof(*req) + count * sizeof(*rpm_msgs);
>
>         req->count = count;
> -       rpm_msgs = req->rpm_msgs;
> +       req->rpm_msgs = rpm_msgs;

I don't really understand what this is fixing either, can you explain?