linux-kernel - Re: [PATCH v2] drm/bridge: ti-sn65dsi86: Fix auxiliary bus lifetime

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Message-ID: <CAE-0n51fbLvobz-R_3LWPZBRg7SNOxgFQ_DYqMo820W_4UOhDA@mail.gmail.com>
Date:   Tue, 13 Jun 2023 11:41:24 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Douglas Anderson <dianders@...omium.org>,
        dri-devel@...ts.freedesktop.org
Cc:     Andrzej Hajda <andrzej.hajda@...el.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...il.com>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Jonas Karlman <jonas@...boo.se>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Robert Foss <rfoss@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] drm/bridge: ti-sn65dsi86: Fix auxiliary bus lifetime

Quoting Douglas Anderson (2023-06-13 06:58:13)
> Memory for the "struct device" for any given device isn't supposed to
> be released until the device's release() is called. This is important
> because someone might be holding a kobject reference to the "struct
> device" and might try to access one of its members even after any
> other cleanup/uninitialization has happened.
>
> Code analysis of ti-sn65dsi86 shows that this isn't quite right. When
> the code was written, it was believed that we could rely on the fact
> that the child devices would all be freed before the parent devices
> and thus we didn't need to worry about a release() function. While I
> still believe that the parent's "struct device" is guaranteed to
> outlive the child's "struct device" (because the child holds a kobject
> reference to the parent), the parent's "devm" allocated memory is a
> different story. That appears to be freed much earlier.
>
> Let's make this better for ti-sn65dsi86 by allocating each auxiliary
> with kzalloc and then free that memory in the release().
>
> Fixes: bf73537f411b ("drm/bridge: ti-sn65dsi86: Break GPIO and MIPI-to-eDP bridge into sub-drivers")
> Suggested-by: Stephen Boyd <swboyd@...omium.org>
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---

Reviewed-by: Stephen Boyd <swboyd@...omium.org>