linux-kernel - Re: [PATCH v1] base: soc: Handle custom soc information sysfs entries

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Date:   Thu, 3 Oct 2019 22:50:57 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Murali Nalajala <mnalajal@...eaurora.org>,
        gregkh@...uxfoundation.org, rafael@...nel.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] base: soc: Handle custom soc information sysfs entries

On Thu 03 Oct 22:38 PDT 2019, Stephen Boyd wrote:

> Quoting Murali Nalajala (2019-10-03 16:51:50)
> > @@ -151,14 +156,16 @@ struct soc_device *soc_device_register(struct soc_device_attribute *soc_dev_attr
> >  
> >         ret = device_register(&soc_dev->dev);
> >         if (ret)
> > -               goto out3;
> > +               goto out4;
> >  
> >         return soc_dev;
> >  
> > -out3:
> > +out4:
> >         ida_simple_remove(&soc_ida, soc_dev->soc_dev_num);
> >         put_device(&soc_dev->dev);
> >         soc_dev = NULL;
> > +out3:
> > +       kfree(soc_attr_groups);
> 
> This code is tricky. put_device(&soc_dev->dev) will call soc_release()
> so we set soc_dev to NULL before calling kfree() on the error path. This
> way we don't doubly free a pointer that the release function will take
> care of. I wonder if the release function could free the ida as well,
> and then we could just make the device_register() failure path call
> put_device() and return ERR_PTR(ret) directly. Then the error path is
> simpler because we can avoid changing two pointers to NULL to avoid the
> double free twice. Or just inline the ida remove and put_device() call
> in the if and then goto out1 to consolidate the error pointer
> conversion.
> 

But if we instead allocates the ida before the soc_dev, wouldn't the
error path be something like?:

foo:
	put_device(&soc_dev->dev);
bar:
	ida_simple_remove(&soc_ida, soc_num);
	return err;


I think we still need two exit paths from soc_device_register()
regardless of moving the ida_simple_remove() into the release, but we
could drop it from the unregister(). So not sure if this is cleaner...

Regards,
Bjorn

> >  out2:
> >         kfree(soc_dev);
> >  out1: