Re: [PATCH v2 2/2] pinctrl: pinmux: Add pinmux-select debugfs file

Drew Fustini
2021-02-10T19:16:04Z

On Wed, Feb 10, 2021 at 10:05:29PM +0300, Dan Carpenter wrote:
> On Wed, Feb 10, 2021 at 07:39:16PM +0100, Geert Uytterhoeven wrote:
> > Hi Dan,
> >
> > On Wed, Feb 10, 2021 at 7:21 PM Dan Carpenter <dan.carpenter@oracle.com> wrote:
> > > 99b2f99aa41aa7 Drew Fustini 2021-02-09 694 buf = devm_kzalloc(pctldev->dev, PINMUX_MAX_NAME * 2, GFP_KERNEL);
> > > 99b2f99aa41aa7 Drew Fustini 2021-02-09 695 if (!buf)
> > > 99b2f99aa41aa7 Drew Fustini 2021-02-09 696 return -ENOMEM;
> > > 99b2f99aa41aa7 Drew Fustini 2021-02-09 697
> > > 99b2f99aa41aa7 Drew Fustini 2021-02-09 698 fname = devm_kzalloc(pctldev->dev, PINMUX_MAX_NAME, GFP_KERNEL);
> > > 99b2f99aa41aa7 Drew Fustini 2021-02-09 699 if (!fname) {
> > > 99b2f99aa41aa7 Drew Fustini 2021-02-09 700 ret = -ENOMEM;
> > > 99b2f99aa41aa7 Drew Fustini 2021-02-09 701 goto free_buf;
> > >
> > > The gotos are out of order. They should be in mirror/reverse order of
> > > the allocations:
> > >
> > > free_gmane:
> > > devm_kfree(pctldev->dev, gname);
> > > free_fname:
> > > devm_kfree(pctldev->dev, fname);
> > > free_buf:
> > > devm_kfree(pctldev->dev, buf);
> > >
> > > But also why do we need to use devm_kfree() at all? I thought the whole
> > > point of devm_ functions was that they are garbage collected
> > > automatically for you. Can we not just delete all error handling and
> > > return -ENOMEM here?
> >
> > No, because the lifetime of the objects allocated here does not match the
> > lifetime of dev. If they're not freed here, they will only be freed when the
> > device is unbound. As the user can access the sysfs files at will, he can
> > OOM the system.
> >
>
> Then why not use vanilla kmalloc()?

Yes, I believe that is the correct approach. The problem was due to my
misunderstanding of when devm_*() was appropriate. In this case, I
should have been using the vanilla allocation as the buffers used in
this debugfs write operation are not tied to the lifetime of the pin
controller device. The are just allocated for internal use inside the
write function.

thanks,
drew