linux-kernel - Re: [PATCH v3 4/8] drm/msm/dpu: use drmm_writeback_connector

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Message-ID: <zw23hgjduxgijown52jyiomungxx4cjyv63qixtnx5nbm3w7xb@2yy65777ydnj>
Date: Tue, 9 Sep 2025 00:26:08 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc: abhinav.kumar@...ux.dev, airlied@...il.com, alexander.deucher@....com,
        amd-gfx@...ts.freedesktop.org, christian.koenig@....com,
        dave.stevenson@...pberrypi.com, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, geert+renesas@...der.be,
        harry.wentland@....com, jani.nikula@...ux.intel.com,
        jessica.zhang@....qualcomm.com, kernel-list@...pberrypi.com,
        kieran.bingham+renesas@...asonboard.com,
        laurent.pinchart+renesas@...asonboard.com,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org, liviu.dudau@....com,
        louis.chauvet@...tlin.com, lumag@...nel.org,
        maarten.lankhorst@...ux.intel.com, magnus.damm@...il.com,
        marijn.suijten@...ainline.org, mcanal@...lia.com, mripard@...nel.org,
        robin.clark@....qualcomm.com, sean@...rly.run, simona@...ll.ch,
        siqueira@...lia.com, sunpeng.li@....com, suraj.kandpal@...el.com,
        tomi.valkeinen+renesas@...asonboard.com, tzimmermann@...e.de
Subject: Re: [PATCH v3 4/8] drm/msm/dpu: use drmm_writeback_connector_init()

On Mon, Sep 08, 2025 at 11:09:07PM +0200, Christophe JAILLET wrote:
> Le 19/08/2025 à 22:32, Dmitry Baryshkov a écrit :
> > Use drmm_plain_encoder_alloc() to allocate simple encoder and
> > drmm_writeback_connector_init() in order to initialize writeback
> > connector instance.
> > 
> > Reviewed-by: Louis Chauvet <louis.chauvet-LDxbnhwyfcJBDgjK7y7TUQ@...lic.gmane.org>
> > Reviewed-by: Suraj Kandpal <suraj.kandpal-ral2JQCrhuEAvxtiuMwx3w@...lic.gmane.org>
> > Reviewed-by: Jessica Zhang <jessica.zhang-5oFBVzJwu8Ry9aJCnZT0Uw@...lic.gmane.org>
> > Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov-5oFBVzJwu8Ry9aJCnZT0Uw@...lic.gmane.org>
> > ---
> >   drivers/gpu/drm/msm/disp/dpu1/dpu_writeback.c | 10 +++-------
> >   1 file changed, 3 insertions(+), 7 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_writeback.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_writeback.c
> > index 8ff496082902b1ee713e806140f39b4730ed256a..cd73468e369a93c50303db2a7d4499bcb17be5d1 100644
> > --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_writeback.c
> > +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_writeback.c
> > @@ -80,7 +80,6 @@ static int dpu_wb_conn_atomic_check(struct drm_connector *connector,
> >   static const struct drm_connector_funcs dpu_wb_conn_funcs = {
> >   	.reset = drm_atomic_helper_connector_reset,
> >   	.fill_modes = drm_helper_probe_single_connector_modes,
> > -	.destroy = drm_connector_cleanup,
> >   	.atomic_duplicate_state = drm_atomic_helper_connector_duplicate_state,
> >   	.atomic_destroy_state = drm_atomic_helper_connector_destroy_state,
> >   };
> > @@ -131,12 +130,9 @@ int dpu_writeback_init(struct drm_device *dev, struct drm_encoder *enc,
> >   	drm_connector_helper_add(&dpu_wb_conn->base.base, &dpu_wb_conn_helper_funcs);
> > -	/* DPU initializes the encoder and sets it up completely for writeback
> > -	 * cases and hence should use the new API drm_writeback_connector_init_with_encoder
> > -	 * to initialize the writeback connector
> > -	 */
> > -	rc = drm_writeback_connector_init_with_encoder(dev, &dpu_wb_conn->base, enc,
> > -			&dpu_wb_conn_funcs, format_list, num_formats);
> > +	rc = drmm_writeback_connector_init(dev, &dpu_wb_conn->base,
> > +					   &dpu_wb_conn_funcs, enc,
> > +					   format_list, num_formats);
> >   	if (!rc)
> >   		dpu_wb_conn->wb_enc = enc;
> > 
> 
> dpu_wb_conn is allocated a few lines above using devm_kzalloc().

That's a valid point, thanks!

> 
> Based on [1], mixing devm_ and drmm_ is not safe and can lead to a uaf.
> 
> Is it correct here?
> If the explanation at [1] is correct, then &dpu_wb_conn->base would point to
> some released memory, IIUC.
> 
> 
> just my 2c.
> 
> CJ
> 
> [1]: https://web.git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/drivers/gpu/drm/xe/xe_hwmon.c?id=3a13c2de442d6bfaef9c102cd1092e6cae22b753

-- 
With best wishes
Dmitry