linux-kernel - Re: [PATCH 1/1] drm/amd/display: handle nulled pipe context in DCE110's set

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Message-ID: <CADnq5_OxGp6AH+H3igpZNs_OK1wN=hu5AkQK9EBwfrJ2T2etLw@mail.gmail.com>
Date: Mon, 16 Sep 2024 17:12:18 -0400
From: Alex Deucher <alexdeucher@...il.com>
To: tjakobi@...h.uni-bielefeld.de
Cc: Harry Wentland <harry.wentland@....com>, Leo Li <sunpeng.li@....com>, 
	Rodrigo Siqueira <Rodrigo.Siqueira@....com>, Alex Deucher <alexander.deucher@....com>, 
	Christian König <christian.koenig@....com>, 
	"Pan, Xinhui" <Xinhui.Pan@....com>, David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, 
	Mario Limonciello <mario.limonciello@....com>, amd-gfx@...ts.freedesktop.org, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] drm/amd/display: handle nulled pipe context in
 DCE110's set_drr()

Acked-by: Alex Deucher <alexander.deucher@....com>

And applied.

Thanks!

On Mon, Sep 16, 2024 at 9:03 AM <tjakobi@...h.uni-bielefeld.de> wrote:
>
> From: Tobias Jakobi <tjakobi@...h.uni-bielefeld.de>
>
> As set_drr() is called from IRQ context, it can happen that the
> pipe context has been nulled by dc_state_destruct().
>
> Apply the same protection here that is already present for
> dcn35_set_drr() and dcn10_set_drr(). I.e. fetch the tg pointer
> first (to avoid a race with dc_state_destruct()), and then
> check the local copy before using it.
>
> Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3142
> Fixes: 06ad7e164256 ("drm/amd/display: Destroy DC context while keeping DML and DML2")
> Signed-off-by: Tobias Jakobi <tjakobi@...h.uni-bielefeld.de>
> ---
>  .../amd/display/dc/hwss/dce110/dce110_hwseq.c | 21 ++++++++++++-------
>  1 file changed, 14 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/display/dc/hwss/dce110/dce110_hwseq.c b/drivers/gpu/drm/amd/display/dc/hwss/dce110/dce110_hwseq.c
> index 0d3ea291eeee..666dfc6d192e 100644
> --- a/drivers/gpu/drm/amd/display/dc/hwss/dce110/dce110_hwseq.c
> +++ b/drivers/gpu/drm/amd/display/dc/hwss/dce110/dce110_hwseq.c
> @@ -1970,13 +1970,20 @@ static void set_drr(struct pipe_ctx **pipe_ctx,
>          * as well.
>          */
>         for (i = 0; i < num_pipes; i++) {
> -               pipe_ctx[i]->stream_res.tg->funcs->set_drr(
> -                       pipe_ctx[i]->stream_res.tg, &params);
> -
> -               if (adjust.v_total_max != 0 && adjust.v_total_min != 0)
> -                       pipe_ctx[i]->stream_res.tg->funcs->set_static_screen_control(
> -                                       pipe_ctx[i]->stream_res.tg,
> -                                       event_triggers, num_frames);
> +               /* dc_state_destruct() might null the stream resources, so fetch tg
> +                * here first to avoid a race condition. The lifetime of the pointee
> +                * itself (the timing_generator object) is not a problem here.
> +                */
> +               struct timing_generator *tg = pipe_ctx[i]->stream_res.tg;
> +
> +               if ((tg != NULL) && tg->funcs) {
> +                       if (tg->funcs->set_drr)
> +                               tg->funcs->set_drr(tg, &params);
> +                       if (adjust.v_total_max != 0 && adjust.v_total_min != 0)
> +                               if (tg->funcs->set_static_screen_control)
> +                                       tg->funcs->set_static_screen_control(
> +                                               tg, event_triggers, num_frames);
> +               }
>         }
>  }
>
> --
> 2.44.2
>