This is a note to let you know that I've just added the patch titled
drm/mediatek: Fix a null pointer crash in mtk_drm_crtc_finish_page_flip
to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
drm-mediatek-fix-a-null-pointer-crash-in-mtk_drm_crt.patch
and it can be found in the queue-6.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 298efcc344a0f01d1bed0d8a856acd953730833e
Author: Hsin-Yi Wang <hsinyi@xxxxxxxxxxxx>
Date: Fri Feb 23 13:23:29 2024 -0800
drm/mediatek: Fix a null pointer crash in mtk_drm_crtc_finish_page_flip
[ Upstream commit c958e86e9cc1b48cac004a6e245154dfba8e163b ]
It's possible that mtk_crtc->event is NULL in
mtk_drm_crtc_finish_page_flip().
pending_needs_vblank value is set by mtk_crtc->event, but in
mtk_drm_crtc_atomic_flush(), it's is not guarded by the same
lock in mtk_drm_finish_page_flip(), thus a race condition happens.
Consider the following case:
CPU1 CPU2
step 1:
mtk_drm_crtc_atomic_begin()
mtk_crtc->event is not null,
step 1:
mtk_drm_crtc_atomic_flush:
mtk_drm_crtc_update_config(
!!mtk_crtc->event)
step 2:
mtk_crtc_ddp_irq ->
mtk_drm_finish_page_flip:
lock
mtk_crtc->event set to null,
pending_needs_vblank set to false
unlock
pending_needs_vblank set to true,
step 2:
mtk_crtc_ddp_irq ->
mtk_drm_finish_page_flip called again,
pending_needs_vblank is still true
//null pointer
Instead of guarding the entire mtk_drm_crtc_atomic_flush(), it's more
efficient to just check if mtk_crtc->event is null before use.
Fixes: 119f5173628a ("drm/mediatek: Add DRM Driver for Mediatek SoC MT8173.")
Signed-off-by: Hsin-Yi Wang <hsinyi@xxxxxxxxxxxx>
Reviewed-by: CK Hu <ck.hu@xxxxxxxxxxxx>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20240223212404.3709690-1-hsinyi@xxxxxxxxxxxx/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/gpu/drm/mediatek/mtk_drm_crtc.c b/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
index 558000db4a100..beaaf44004cfd 100644
--- a/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
+++ b/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
@@ -91,11 +91,13 @@ static void mtk_drm_crtc_finish_page_flip(struct mtk_drm_crtc *mtk_crtc)
struct drm_crtc *crtc = &mtk_crtc->base;
unsigned long flags;
- spin_lock_irqsave(&crtc->dev->event_lock, flags);
- drm_crtc_send_vblank_event(crtc, mtk_crtc->event);
- drm_crtc_vblank_put(crtc);
- mtk_crtc->event = NULL;
- spin_unlock_irqrestore(&crtc->dev->event_lock, flags);
+ if (mtk_crtc->event) {
+ spin_lock_irqsave(&crtc->dev->event_lock, flags);
+ drm_crtc_send_vblank_event(crtc, mtk_crtc->event);
+ drm_crtc_vblank_put(crtc);
+ mtk_crtc->event = NULL;
+ spin_unlock_irqrestore(&crtc->dev->event_lock, flags);
+ }
}
static void mtk_drm_finish_page_flip(struct mtk_drm_crtc *mtk_crtc)
