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
