Re: [PATCH 1/3] drm: Restore driver.preclose() for all to use

[Daniel Vetter <daniel@ffwll.ch>]

On Thu, Jul 23, 2020 at 7:21 PM Chris Wilson <chris@chris-wilson.co.uk> wrote:
>
> An unfortunate sequence of events, but it turns out there is a valid
> usecase for being able to free/decouple the driver objects before they
> are freed by the DRM core. In particular, if we have a pointer into a
> drm core object from inside a driver object, that pointer needs to be
> nerfed *before* it is freed so that concurrent access (e.g. debugfs)
> does not following the dangling pointer.
>
> The legacy marker was adding in the code movement from drp_fops.c to
> drm_file.c

I might fumble a lot, but not this one:

commit 45c3d213a400c952ab7119f394c5293bb6877e6b
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Mon May 8 10:26:33 2017 +0200

    drm: Nerf the preclose callback for modern drivers

Also looking at the debugfs hook that has some rather adventurous
stuff going on I think, feels a bit like a kitchensink with batteries
included. If that's really all needed I'd say iterate the contexts by
first going over files, then the ctx (which arent shared anyway) and
the problem should also be gone.
-Daniel

> References: 9acdac68bcdc ("drm: rename drm_fops.c to drm_file.c")
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Gustavo Padovan <gustavo.padovan@collabora.com>
> Cc: CQ Tang <cq.tang@intel.com>
> Cc: <stable@vger.kernel.org> # v4.12+
> ---
>  drivers/gpu/drm/drm_file.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
> index 0ac4566ae3f4..7b4258d6f7cc 100644
> --- a/drivers/gpu/drm/drm_file.c
> +++ b/drivers/gpu/drm/drm_file.c
> @@ -258,8 +258,7 @@ void drm_file_free(struct drm_file *file)
>                   (long)old_encode_dev(file->minor->kdev->devt),
>                   atomic_read(&dev->open_count));
>
> -       if (drm_core_check_feature(dev, DRIVER_LEGACY) &&
> -           dev->driver->preclose)
> +       if (dev->driver->preclose)
>                 dev->driver->preclose(dev, file);
>
>         if (drm_core_check_feature(dev, DRIVER_LEGACY))
> --
> 2.20.1
>
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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