Re: [PATCH] drm/mediatek: Fix a null pointer crash in mtk_drm_crtc_finish_page_flip
Re: [PATCH] drm/mediatek: Fix a null pointer crash in mtk_drm_crtc_finish_page_flip
Hi, Hsin-yi:
On Fri, 2024-02-23 at 13:23 -0800, Hsin-Yi Wang wrote:
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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.
Signed-off-by: Hsin-Yi Wang mailto:hsi...@chromium.org>>
Fixes: 119f5173628a ("drm/mediatek: Add DRM Driver for Mediatek SoC MT8173.")
Reviewed-by: CK Hu
---
drivers/gpu/drm/mediatek/mtk_drm_crtc.c | 12 +++-
1 file changed, 7 insertions(+), 5 deletions(-)
diff --git a/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
b/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
index db43f9dff912..d645b85f9721 100644
--- a/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
+++ b/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
@@ -95,11 +95,13 @@ 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)
--
2.44.0.rc0.258.g7320e95886-goog
[PATCH] drm/mediatek: Fix a null pointer crash in mtk_drm_crtc_finish_page_flip
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.
Signed-off-by: Hsin-Yi Wang
Fixes: 119f5173628a ("drm/mediatek: Add DRM Driver for Mediatek SoC MT8173.")
---
drivers/gpu/drm/mediatek/mtk_drm_crtc.c | 12 +++-
1 file changed, 7 insertions(+), 5 deletions(-)
diff --git a/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
b/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
index db43f9dff912..d645b85f9721 100644
--- a/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
+++ b/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
@@ -95,11 +95,13 @@ 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)
--
2.44.0.rc0.258.g7320e95886-goog
