[PATCH] coresight: potential uninitialized variable in probe()

[PATCH] coresight: potential uninitialized variable in probe()

[Dan Carpenter]

The "drvdata->atclk" clock is optional, but if it gets set to an error
pointer then we're accidentally return an uninitialized variable instead
of success.

Fixes: 78e6427b4e7b ("coresight: funnel: Support static funnel")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
---
 drivers/hwtracing/coresight/coresight-funnel.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/hwtracing/coresight/coresight-funnel.c b/drivers/hwtracing/coresight/coresight-funnel.c
index 5867fcb4503b..fa97cb9ab4f9 100644
--- a/drivers/hwtracing/coresight/coresight-funnel.c
+++ b/drivers/hwtracing/coresight/coresight-funnel.c
@@ -244,6 +244,7 @@ static int funnel_probe(struct device *dev, struct resource *res)
 	}
 
 	pm_runtime_put(dev);
+	ret = 0;
 
 out_disable_clk:
 	if (ret && !IS_ERR_OR_NULL(drvdata->atclk))
-- 
2.20.1


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Re: [PATCH] coresight: potential uninitialized variable in probe()

[Leo Yan]

Hi Dan,

On Wed, Jun 12, 2019 at 11:58:15PM -0700, Dan Carpenter wrote:
> The "drvdata->atclk" clock is optional, but if it gets set to an error
> pointer then we're accidentally return an uninitialized variable instead
> of success.

You are right, thanks a lot for pointing out.

I'd like to initialize 'ret = 0' at the head of function, so we can
has the same fashion with other CoreSight drivers (e.g. replicator).

 static int funnel_probe(struct device *dev, struct resource *res)
 {
-	int ret;
+	int ret = 0;

If you agree, could you send a new patch for this?

Thanks,
Leo Yan

> Fixes: 78e6427b4e7b ("coresight: funnel: Support static funnel")
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> ---
>  drivers/hwtracing/coresight/coresight-funnel.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-funnel.c b/drivers/hwtracing/coresight/coresight-funnel.c
> index 5867fcb4503b..fa97cb9ab4f9 100644
> --- a/drivers/hwtracing/coresight/coresight-funnel.c
> +++ b/drivers/hwtracing/coresight/coresight-funnel.c
> @@ -244,6 +244,7 @@ static int funnel_probe(struct device *dev, struct resource *res)
>  	}
>  
>  	pm_runtime_put(dev);
> +	ret = 0;
>  
>  out_disable_clk:
>  	if (ret && !IS_ERR_OR_NULL(drvdata->atclk))
> -- 
> 2.20.1
> 

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Re: [PATCH] coresight: potential uninitialized variable in probe()

[Dan Carpenter]

On Thu, Jun 13, 2019 at 03:49:22PM +0800, Leo Yan wrote:
> Hi Dan,
> 
> On Wed, Jun 12, 2019 at 11:58:15PM -0700, Dan Carpenter wrote:
> > The "drvdata->atclk" clock is optional, but if it gets set to an error
> > pointer then we're accidentally return an uninitialized variable instead
> > of success.
> 
> You are right, thanks a lot for pointing out.
> 
> I'd like to initialize 'ret = 0' at the head of function, so we can
> has the same fashion with other CoreSight drivers (e.g. replicator).
> 
>  static int funnel_probe(struct device *dev, struct resource *res)
>  {
> -	int ret;
> +	int ret = 0;
> 
> If you agree, could you send a new patch for this?

Obviously that's an option I considered...  The reason I didn't go with
that is that a common bug that I see is:

	int ret = 0;

	p = kmalloc();
	if (!p)
		goto free_whatever;

In my experience it's better to initialize the return as late as
possible so that you get static checker warnings when you forget to set
the error code.

Also I think my way is more readable.  I like to make the success path
as explicit as possible.  I hate when people do things like:

	if (!ret)
		return ret;

About 10% of the time when you see this it is a bug, but it's hard to
tell because it's not readable like it would be if people did:

	if (!ret)
		return 0;

Or sometimes you see things like:

	if (corner_case)
		goto free; /* success path */

Without the "/* success path */ comment explaining why we're returning
zero most readers will assume it's a mistake.

regards,
dan carpenter

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Re: [PATCH] coresight: potential uninitialized variable in probe()

[Leo Yan]

Hi Dan,

On Thu, Jun 13, 2019 at 11:14:19AM +0300, Dan Carpenter wrote:
> On Thu, Jun 13, 2019 at 03:49:22PM +0800, Leo Yan wrote:
> > Hi Dan,
> > 
> > On Wed, Jun 12, 2019 at 11:58:15PM -0700, Dan Carpenter wrote:
> > > The "drvdata->atclk" clock is optional, but if it gets set to an error
> > > pointer then we're accidentally return an uninitialized variable instead
> > > of success.
> > 
> > You are right, thanks a lot for pointing out.
> > 
> > I'd like to initialize 'ret = 0' at the head of function, so we can
> > has the same fashion with other CoreSight drivers (e.g. replicator).
> > 
> >  static int funnel_probe(struct device *dev, struct resource *res)
> >  {
> > -	int ret;
> > +	int ret = 0;
> > 
> > If you agree, could you send a new patch for this?
> 
> Obviously that's an option I considered...  The reason I didn't go with
> that is that a common bug that I see is:
> 
> 	int ret = 0;
> 
> 	p = kmalloc();
> 	if (!p)
> 		goto free_whatever;
> 
> In my experience it's better to initialize the return as late as
> possible so that you get static checker warnings when you forget to set
> the error code.

Just want to check one thing, which static checker you are using?
I use sparse but it doesn't report this issue (I learned coccinelle
also can do this but it outputs verbose logs).

To be honest, I didn't often run static checker when committed patches,
but hope later can improve for this.

> Also I think my way is more readable.  I like to make the success path
> as explicit as possible.  I hate when people do things like:
> 
> 	if (!ret)
> 		return ret;
> 
> About 10% of the time when you see this it is a bug, but it's hard to
> tell because it's not readable like it would be if people did:
> 
> 	if (!ret)
> 		return 0;
> 
> Or sometimes you see things like:
> 
> 	if (corner_case)
> 		goto free; /* success path */
> 
> Without the "/* success path */ comment explaining why we're returning
> zero most readers will assume it's a mistake.

Thanks for sharing much knowledge; your change is okay for me.

I think the point is the good habit can avoid pitfall and traps :) [1]

Thanks,
Leo Yan

[1] https://www.amazon.com/C-Traps-Pitfalls-Andrew-Koenig/dp/0201179288

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Re: [PATCH] coresight: potential uninitialized variable in probe()

[Leo Yan]

On Thu, Jun 13, 2019 at 05:56:37PM +0800, Leo Yan wrote:

[...]

> > In my experience it's better to initialize the return as late as
> > possible so that you get static checker warnings when you forget to set
> > the error code.
> 
> Just want to check one thing, which static checker you are using?

Okay, I think it's smatch :)

Thanks,
Leo Yan

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Re: [PATCH] coresight: potential uninitialized variable in probe()

[Mathieu Poirier]

On Thu, 13 Jun 2019 at 00:59, Dan Carpenter <dan.carpenter@oracle.com> wrote:
>
> The "drvdata->atclk" clock is optional, but if it gets set to an error
> pointer then we're accidentally return an uninitialized variable instead
> of success.
>
> Fixes: 78e6427b4e7b ("coresight: funnel: Support static funnel")
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> ---
>  drivers/hwtracing/coresight/coresight-funnel.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/drivers/hwtracing/coresight/coresight-funnel.c b/drivers/hwtracing/coresight/coresight-funnel.c
> index 5867fcb4503b..fa97cb9ab4f9 100644
> --- a/drivers/hwtracing/coresight/coresight-funnel.c
> +++ b/drivers/hwtracing/coresight/coresight-funnel.c
> @@ -244,6 +244,7 @@ static int funnel_probe(struct device *dev, struct resource *res)
>         }
>
>         pm_runtime_put(dev);
> +       ret = 0;

Applied - thanks.

>
>  out_disable_clk:
>         if (ret && !IS_ERR_OR_NULL(drvdata->atclk))
> --
> 2.20.1
>

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