Re: [PATCH v5 5/7] revocable: Add fops replacement

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

On Thu, Dec 11, 2025 at 05:36:57PM +0900, Wolfram Sang wrote:
> 
> > > Isn't there even prototype code from Dan Williams?
> > > 
> > > "[PATCH 1/3] cdev: Finish the cdev api with queued mode support"
> > > 
> > > https://lkml.org/lkml/2021/1/20/997
> > 
> > I mentioned that in my LPC talk in 2022 :-) I think we should merge that
> > (or a rebased, possibly improved version of it). I've meant to try
> > plumbing that series in V4L2 but couldn't find the time so far.
> 
> Yes, you mentioned it in 2022 but maybe not everyone in this thread is
> right now aware of it ;) The patch above got changes requested. I talked
> to Dan very briefly about it at Maintainers Summit 2023 and he was also
> open (back then) to pick it up again.

After discussing with Tzung-Bi today after his presentation (thank you
Tzung-Bi for your time, it helped me understand the problem you're
facing better), I wonder if this series is fixing the issue in the right
place.

At the core of the problem is a devm_kzalloc() call to allocate
driver-specific data. That data structure is then referenced from a
cdev, which can dereference is after it gets freed. It seems that
reference-counting the data structure instead of using devm_kzalloc()
could be a better solution.

-- 
Regards,

Laurent Pinchart