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

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Message-ID: <654e04e3-d80e-4d34-a1a0-21f66d43875b@wanadoo.fr>
Date: Mon, 8 Sep 2025 23:38:44 +0200
From: Christophe JAILLET <christophe.jaillet@...adoo.fr>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
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()

Le 08/09/2025 à 23:26, Dmitry Baryshkov a écrit :
> 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-XMD5yJDbdMReXY1tMh2IBg@...lic.gmane.org>
>>> Reviewed-by: Suraj Kandpal <suraj.kandpal-ral2JQCrhuEAvxtiuMwx3w-XMD5yJDbdMReXY1tMh2IBg@...lic.gmane.org>
>>> Reviewed-by: Jessica Zhang <jessica.zhang-5oFBVzJwu8Ry9aJCnZT0Uw-XMD5yJDbdMReXY1tMh2IBg@...lic.gmane.org>
>>> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov-5oFBVzJwu8Ry9aJCnZT0Uw-XMD5yJDbdMReXY1tMh2IBg@...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!

I've not analyzed in details all the patches of the serie, but at least 
patch 2/8 and 6/8 seems to have the same pattern.

CJ

> 
>>
>> 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
>