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SubjectRe: [PATCH v2 16/23] counter: interrupt-cnt: Convert to new counter registration
On Mon, Dec 27, 2021 at 12:21:14PM +0100, Lars-Peter Clausen wrote:
> On 12/27/21 11:59 AM, Greg Kroah-Hartman wrote:
> > On Mon, Dec 27, 2021 at 10:45:19AM +0100, Uwe Kleine-König wrote:
> > > This fixes device lifetime issues where it was possible to free a live
> > > struct device.
> > >
> > > Fixes: a55ebd47f21f ("counter: add IRQ or GPIO based counter")
> > > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
> > > ---
> > > drivers/counter/interrupt-cnt.c | 28 ++++++++++++++++------------
> > > 1 file changed, 16 insertions(+), 12 deletions(-)
> > >
> > > diff --git a/drivers/counter/interrupt-cnt.c b/drivers/counter/interrupt-cnt.c
> > > index 4bf706ef46e2..9e99702470c2 100644
> > > --- a/drivers/counter/interrupt-cnt.c
> > > +++ b/drivers/counter/interrupt-cnt.c
> > > @@ -16,7 +16,6 @@
> > > struct interrupt_cnt_priv {
> > > atomic_t count;
> > > - struct counter_device counter;
> > > struct gpio_desc *gpio;
> > > int irq;
> > > bool enabled;
> > > @@ -148,12 +147,14 @@ static const struct counter_ops interrupt_cnt_ops = {
> > > static int interrupt_cnt_probe(struct platform_device *pdev)
> > > {
> > > struct device *dev = &pdev->dev;
> > > + struct counter_device *counter;
> > > struct interrupt_cnt_priv *priv;
> > > int ret;
> > > - priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
> > > - if (!priv)
> > > + counter = devm_counter_alloc(dev, sizeof(*priv));
> > I just picked one of these patches at random, nothing specific about
> > this driver...
> >
> > You can not have a 'struct device' in memory allocated by devm_*()
> > functions for the obvious reason that now that memory is being
> > controlled by a reference count that is OUTSIDE of the structure itself.
> >
> > So while your goal might be good here, this is not the correct solution
> > at all, sorry.
>
> Before this patch the memory for the struct device was devm_kzalloc'ed.
> Which as you point out is a bug.
>
> After this patch the memory is reference counted and will be freed when the
> last reference is dropped, in the release callback of the struct device.
>
> The alloc function is still a devm_ function, but on 'free' it will only
> drop the reference to the struct device that it holds. This is a very common
> pattern that is used by basically any driver subsystem in the kernel.

Then it is not a real devm_() call, let's not call it that please as it
is obviously very confusing :)

Just call it counter_alloc(), or , counter_create(), or something a bit
more in line with the rest of all driver subsystems.

thanks,

greg k-h

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