linux-kernel - Re: [PATCH] drm/vc4: Fix atomicity violation in vc4_crtc_send

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Message-ID: <CANgpojXKgZXjeCO9MYr83=p-Kz0_Migm4c9-4qTidHYp=G+fMg@mail.gmail.com>
Date: Tue, 24 Sep 2024 20:01:06 +0800
From: Qiu-ji Chen <chenqiuji666@...il.com>
To: Qiu-ji Chen <chenqiuji666@...il.com>, mripard@...nel.org, 
	dave.stevenson@...pberrypi.com, kernel-list@...pberrypi.com, 
	maarten.lankhorst@...ux.intel.com, tzimmermann@...e.de, airlied@...il.com, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	baijiaju1990@...il.com, stable@...r.kernel.org, simona.vetter@...ll.ch
Cc: daniel@...ll.ch
Subject: Re: [PATCH] drm/vc4: Fix atomicity violation in vc4_crtc_send_vblank()

Hi,

In the drm_device structure, it is mentioned: "@event_lock: Protects
@vblank_event_list and event delivery in general." I believe that the
validity check and the subsequent null assignment operation are part
of the event delivery process, and all of these should be protected by
the event_lock. If there is no lock protection before the validity
check, it is possible for a null crtc->state->event to be passed into
the drm_crtc_send_vblank_event() function, leading to a null pointer
dereference error.

We have observed its callers and found that they are from the
drm_crtc_helper_funcs driver interface. We believe that functions
within driver interfaces can be concurrent, potentially causing a data
race on crtc->state->event.

Qiu-ji Chen