linux-kernel - Re: [PATCH v1 1/2] media: hi846: fix usage of pm_runtime_get_if_in

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Date:   Fri, 07 Apr 2023 15:31:02 +0200
From:   Martin Kepplinger <martin.kepplinger@...i.sm>
To:     Sakari Ailus <sakari.ailus@....fi>
Cc:     mchehab@...nel.org, laurent.pinchart@...asonboard.com,
        kernel@...i.sm, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/2] media: hi846: fix usage of
 pm_runtime_get_if_in_use()

Am Mittwoch, dem 05.04.2023 um 15:52 +0300 schrieb Sakari Ailus:
> Hi Martin,
> 
> On Wed, Apr 05, 2023 at 11:29:03AM +0200, Martin Kepplinger wrote:
> > pm_runtime_get_if_in_use() does not only return nonzero values when
> > the device is in use, it can return a negative errno too.
> > 
> > And especially during resuming from system suspend, when runtime pm
> > is not yet up again, this can very well happen. And in such a case
> > the subsequent pm_runtime_put() call would result in a refcount
> > underflow!
> 
> I think this issue should have a more generic solution, it's very
> difficult
> to address this in drivers only with the current APIs.
> 
> pm_runtime_get_if_in_use() will also return an error if runtime PM is
> disabled, so this patch will break the driver for that configuration.

ok but the driver is currently broken for any *other* error returned by
pm_runtime_get_if_in_use() (than the runtime-PM disabled error).

The execution-path during system-resume I'm interested in gets -EAGAIN
here. Would it be ok for you if I'd return early only for that one
error only here?


> 
> > 
> > Fix it by correctly using pm_runtime_get_if_in_use().
> > 
> > Signed-off-by: Martin Kepplinger <martin.kepplinger@...i.sm>
> > ---
> >  drivers/media/i2c/hi846.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/media/i2c/hi846.c b/drivers/media/i2c/hi846.c
> > index 5b5ea5425e984..0b0eda2e223cd 100644
> > --- a/drivers/media/i2c/hi846.c
> > +++ b/drivers/media/i2c/hi846.c
> > @@ -1544,7 +1544,7 @@ static int hi846_set_ctrl(struct v4l2_ctrl
> > *ctrl)
> >                                          exposure_max);
> >         }
> >  
> > -       if (!pm_runtime_get_if_in_use(&client->dev))
> > +       if (pm_runtime_get_if_in_use(&client->dev) <= 0)
> >                 return 0;
> >  
> >         switch (ctrl->id) {
>