From: Hsin-Yi Wang <hsinyi@chromium.org> To: Chun-Kuang Hu <chunkuang.hu@kernel.org> Cc: Philipp Zabel <p.zabel@pengutronix.de>, David Airlie <airlied@gmail.com>, Daniel Vetter <daniel@ffwll.ch>, Matthias Brugger <matthias.bgg@gmail.com>, AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>, dri-devel@lists.freedesktop.org, linux-mediatek@lists.infradead.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: [PATCH] drm/mediatek: Fix a null pointer crash in mtk_drm_crtc_finish_page_flip Date: Fri, 23 Feb 2024 13:23:29 -0800 [thread overview] Message-ID: <20240223212404.3709690-1-hsinyi@chromium.org> (raw) 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 <hsinyi@chromium.org> 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
WARNING: multiple messages have this Message-ID (diff)
From: Hsin-Yi Wang <hsinyi@chromium.org> To: Chun-Kuang Hu <chunkuang.hu@kernel.org> Cc: Philipp Zabel <p.zabel@pengutronix.de>, David Airlie <airlied@gmail.com>, Daniel Vetter <daniel@ffwll.ch>, Matthias Brugger <matthias.bgg@gmail.com>, AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>, dri-devel@lists.freedesktop.org, linux-mediatek@lists.infradead.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: [PATCH] drm/mediatek: Fix a null pointer crash in mtk_drm_crtc_finish_page_flip Date: Fri, 23 Feb 2024 13:23:29 -0800 [thread overview] Message-ID: <20240223212404.3709690-1-hsinyi@chromium.org> (raw) 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 <hsinyi@chromium.org> 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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next reply other threads:[~2024-02-23 21:24 UTC|newest] Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top 2024-02-23 21:23 Hsin-Yi Wang [this message] 2024-02-23 21:23 ` [PATCH] drm/mediatek: Fix a null pointer crash in mtk_drm_crtc_finish_page_flip Hsin-Yi Wang 2024-02-27 7:33 ` CK Hu (胡俊光) 2024-02-27 8:14 ` CK Hu (胡俊光) 2024-02-27 8:14 ` CK Hu (胡俊光) 2024-02-27 8:14 ` CK Hu (胡俊光)
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