linux-kernel - Re: [PATCH v2 01/16] drm/panel: get/put panel reference in drm_panel

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Message-ID: <20250620103353.5b43b86f@booty>
Date: Fri, 20 Jun 2025 10:33:53 +0200
From: Luca Ceresoli <luca.ceresoli@...tlin.com>
To: Anusha Srivatsa <asrivats@...hat.com>
Cc: Neil Armstrong <neil.armstrong@...aro.org>, Jessica Zhang
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Subject: Re: [PATCH v2 01/16] drm/panel: get/put panel reference in
 drm_panel_add/remove()

Hello Anusha,

On Thu, 19 Jun 2025 14:15:53 -0500
Anusha Srivatsa <asrivats@...hat.com> wrote:

> Take the panel reference and put it back as required.
> drm_panel_add() and drm_panel_remove() add a panel to
> the global registry and removes a panel respectively.
> Use get() and put() helpers to keep up with refcounting.
> 
> Reviewed-by: Luca Ceresoli <luca.ceresoli@...tlin.com>
> Signed-off-by: Anusha Srivatsa <asrivats@...hat.com>

This patch is good.

I'd just point out that this must be applied only after all drivers
have been converted to the the _alloc API, otherwise with the following
sequence:

  panel = devm_kzalloc();
  drm_panel_init(panel);
  drm_panel_add(panel);
  ...
  drm_panel_remove(panel); <-----

at the drm_panel_remove() you'd have a warning:

  refcount_t: addition on 0; use-after-free.

So, if all panel drivers are converted:
Reviewed-by: Luca Ceresoli <luca.ceresoli@...tlin.com>

-- 
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com