linux-kernel - Re: [PATCH] drm/msm/dp: move add fail safe mode to dp_connector_get

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Date:   Fri, 22 Apr 2022 17:02:33 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Kuogee Hsieh <quic_khsieh@...cinc.com>, agross@...nel.org,
        airlied@...ux.ie, bjorn.andersson@...aro.org, daniel@...ll.ch,
        dmitry.baryshkov@...aro.org, robdclark@...il.com, sean@...rly.run,
        vkoul@...nel.org
Cc:     quic_abhinavk@...cinc.com, quic_aravindh@...cinc.com,
        quic_sbillaka@...cinc.com, freedreno@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/msm/dp: move add fail safe mode to dp_connector_get_mode()

Quoting Kuogee Hsieh (2022-04-22 16:45:23)
> Current DP driver implementation has adding safe mode done at
> dp_hpd_plug_handle() which is expected to be executed under event
> thread context.
>
> However there is possible circular locking happen (see blow stack trace)
> after edp driver call dp_hpd_plug_handle() from dp_bridge_enable() which
> is executed under drm_thread context.
>
> To break this circular locking, this patch have safe mode added at
> dp_connector_get_mode() which is executed under drm thread context.
> Therefore no lock acquired required for &dev->mode_config.mutex while
> adding fail safe mode since it has been hold by drm thread already.

Reported-by: Douglas Anderson <dianders@...omium.org>
Fixes: 8b2c181e3dcf ("drm/msm/dp: add fail safe mode outside of
event_mutex context")
Reviewed-by: Stephen Boyd <swboyd@...omium.org>