Re: clk: change clk_ops' ->determine_rate() prototype

[Boris Brezillon <boris.brezillon@free-electrons.com>]

Dan, Stephen,

Sorry for the late reply, I was away for a couple of days.

On Mon, 13 Jul 2015 15:41:15 -0700
Stephen Boyd <sboyd@codeaurora.org> wrote:

> On 07/10/2015 01:26 AM, Dan Carpenter wrote:
> > Hello Boris Brezillon,
> >
> > This is a semi-automatic email about new static checker warnings.
> >
> > The patch 4a7c639697ef: "clk: change clk_ops' ->determine_rate()
> > prototype" from Jul 7, 2015, leads to the following Smatch complaint:
> >
> > drivers/clk/clk.c:458 clk_mux_determine_rate_flags()
> > 	 error: we previously assumed 'parent' could be null (see line 452)
> >
> > drivers/clk/clk.c
> >     451			if (core->flags & CLK_SET_RATE_PARENT) {
> >     452				ret = __clk_determine_rate(parent ? parent->hw : NULL,
> >                                                             ^^^^^^
> > Check for NULL.
> >
> >     453							   &parent_req);
> >     454				if (ret)
> >     455					return ret;
> >     456	
> >     457				best = parent_req.rate;
> >     458				req->best_parent_hw = parent->hw;
> >                                                        ^^^^^^^^^^
> > Patch adds unchecked dereference.

Yes, you're absolutely right.

> >
> >     459				req->best_parent_rate = best;
> >     460			} else if (parent) {
> >
> >
> 
> Thanks Dan.
> 
> Boris,
> 
> It looks like the transformation here isn't equivalent. If parent is 
> NULL here and we don't crash, parent_req->rate == req->rate and before 
> this patch req->rate would be 0 instead. How about this patch squashed 
> in? It includes some of the removals of best_parent_* assignments that 
> you had in your follow-up patch, because those make it equivalent to the 
> previous code.

And yes, I noticed some instructions were useless while reworking the
determine_rate implementation to return error codes instead of 0, and
the patch you're proposing here looks good to me. Feel free to squash it
with the previous one.


Thanks to both of you.

Best Regards,

Boris

> 
> ------8<----
> 
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index c182d8a7924e..244a6535c69c 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -455,16 +455,10 @@ clk_mux_determine_rate_flags(struct clk_hw *hw, struct clk_rate_request *req,
>   				return ret;
>   
>   			best = parent_req.rate;
> -			req->best_parent_hw = parent->hw;
> -			req->best_parent_rate = best;
>   		} else if (parent) {
>   			best = clk_core_get_rate_nolock(parent);
> -			req->best_parent_hw = parent->hw;
> -			req->best_parent_rate = best;
>   		} else {
>   			best = clk_core_get_rate_nolock(core);
> -			req->best_parent_hw = NULL;
> -			req->best_parent_rate = 0;
>   		}
>   
>   		goto out;
> @@ -810,8 +804,10 @@ static int clk_core_round_rate_nolock(struct clk_core *core,
>    */
>   int __clk_determine_rate(struct clk_hw *hw, struct clk_rate_request *req)
>   {
> -	if (!hw)
> +	if (!hw) {
> +		req->rate = 0;
>   		return 0;
> +	}
>   
>   	return clk_core_round_rate_nolock(hw->core, req);
>   }
> 



-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com