Messages in this thread | | | Date | Tue, 19 Sep 2023 13:00:33 +0200 | Subject | Re: [PATCH] drm/mediatek: Add spinlock for setting vblank event in atomic_begin | From | AngeloGioacchino Del Regno <> |
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Il 19/09/23 09:37, Jason-JH Lin (林睿祥) ha scritto: > Hi Angelo > > Thanks for the reviews. > > Hi Fei, > > Thanks for the testing. > > On Mon, 2023-09-18 at 18:47 +0800, Fei Shao wrote: >> >> External email : Please do not click links or open attachments until >> you have verified the sender or the content. >> Hi Angelo, >> >> On Wed, Sep 13, 2023 at 4:35 PM AngeloGioacchino Del Regno >> <angelogioacchino.delregno@collabora.com> wrote: >>> >>> Il 22/08/23 15:26, Jason-JH.Lin ha scritto: >>>> Add spinlock protection to avoid race condition on vblank event >>>> between mtk_drm_crtc_atomic_begin() and >> mtk_drm_finish_page_flip(). >>>> >>> >>> Hello Jason, >>> >>> Can you please provide more information about this race condition? >>> (check below) >>> >>>> Fixes: 119f5173628a ("drm/mediatek: Add DRM Driver for Mediatek >> SoC MT8173.") >>>> Signed-off-by: Jason-JH.Lin <jason-jh.lin@mediatek.com> >>>> --- >>>> drivers/gpu/drm/mediatek/mtk_drm_crtc.c | 5 +++++ >>>> 1 file changed, 5 insertions(+) >>>> >>>> diff --git a/drivers/gpu/drm/mediatek/mtk_drm_crtc.c >> b/drivers/gpu/drm/mediatek/mtk_drm_crtc.c >>>> index d40142842f85..128a672fe3c9 100644 >>>> --- a/drivers/gpu/drm/mediatek/mtk_drm_crtc.c >>>> +++ b/drivers/gpu/drm/mediatek/mtk_drm_crtc.c >>>> @@ -746,6 +746,9 @@ static void mtk_drm_crtc_atomic_begin(struct >> drm_crtc *crtc, >>> >>> >> crtc); >>>> struct mtk_crtc_state *mtk_crtc_state = >> to_mtk_crtc_state(crtc_state); >>>> struct mtk_drm_crtc *mtk_crtc = to_mtk_crtc(crtc); >>>> + unsigned long flags; >>>> + >>>> + spin_lock_irqsave(&crtc->dev->event_lock, flags); >>>> >>>> if (mtk_crtc->event && mtk_crtc_state->base.event) >>>> DRM_ERROR("new event while there is still a pending >> event\n"); >>>> @@ -756,6 +759,8 @@ static void mtk_drm_crtc_atomic_begin(struct >> drm_crtc *crtc, >>> >>> ...because my suspect is that what creates the race condition in >> this function is >>> the unlocked *assignment* to mtk_crtc->event, not the rest. >>> >>> If I'm right, you don't need to unconditionally spinlock at the >> beginning of this >>> function hence ever-so-slightly improving performance compared to >> this version. >>> >>> Can you please try this one and check if this *also* solves the >> issue? >>> >>> if (mtk_crtc_state->base.event) { >>> mtk_crtc_state->base.event->pipe = >> drm_crtc_index(crtc); >>> WARN_ON(drm_crtc_vblank_get(crtc) != 0); >>> >>> spin_lock_irqsave(&crtc->dev->event_lock, flags); >>> mtk_crtc->event = mtk_crtc_state->base.event; >>> spin_lock_irqrestore(&crtc->dev->event_lock, >> flags); >>> >>> mtk_crtc_state->base.event = NULL; >>> } >>> >>> P.S.: I'd try that myself, but I can't seem to reproduce the issue. >> > I can't reproduce the system hang issue reported from customer by > toggling the night light mode in UI panel either. > But I can see the error message "new event while there is still a > pending event" when I was reproducing the issue. > > Here is the debug info from "Wei-Shun <weishunc@google.com>": > > From the kernel tracing: > 99342.377173: mtk_crtc_ddp_irq <-mtk_disp_ovl_irq_handler > 99342.377226: > drm_crtc_send_vblank_event <-mtk_crtc_ddp_irq > 99342.393831: > mtk_crtc_ddp_irq <-mtk_disp_ovl_irq_handler > 99342.393887: > drm_crtc_send_vblank_event <-mtk_crtc_ddp_irq > 99342.410469: > mtk_crtc_ddp_irq <-mtk_disp_ovl_irq_handler > 99342.410519: > drm_crtc_send_vblank_event <-mtk_crtc_ddp_irq > 99342.427094: > mtk_crtc_ddp_irq <-mtk_disp_ovl_irq_handler > 99342.443831: > mtk_crtc_ddp_irq <-mtk_disp_ovl_irq_handler > 99342.460495: > mtk_crtc_ddp_irq <-mtk_disp_ovl_irq_handler > 99342.477157: > mtk_crtc_ddp_irq <-mtk_disp_ovl_irq_handler > 99342.493841: > mtk_crtc_ddp_irq <-mtk_disp_ovl_irq_handler > 99342.510453: > mtk_crtc_ddp_irq <-mtk_disp_ovl_irq_handler > > Every mtk_crtc_ddp_irq should come with a drm_crtc_send_vblank_event. > However, when the issue happens, the mtk_crtc_ddp_irq keeps firing but > no drm_crtc_send_vblank_event. I suspect this is the main reason > causing flip_done timeout. > > In mtk_drm_crtc.c, mtk_crtc->config_updating and mtk_crtc- >> pending_needs_vblank are the conditions that may impact the vblank > event. > > static void mtk_drm_finish_page_flip(struct mtk_drm_crtc *mtk_crtc) > { > struct drm_crtc *crtc = &mtk_crtc->base; > unsigned long flags; > > drm_crtc_handle_vblank(&mtk_crtc->base); > > spin_lock_irqsave(&crtc->dev->event_lock, flags); > ==> if (!mtk_crtc->config_updating && mtk_crtc->pending_needs_vblank) { > mtk_drm_crtc_finish_page_flip(mtk_crtc); > mtk_crtc->pending_needs_vblank = false; > } > spin_unlock_irqrestore(&crtc->dev->event_lock, flags); > } > > > There are 3 lines are called in mtk_drm_crtc_finish_page_flip(): > drm_crtc_send_vblank_event(crtc, mtk_crtc->event); > drm_crtc_vblank_put(crtc); > mtk_crtc->event = NULL; > > So I want to protect these 3 things to avoid them encountering race > conditions: > mtk_crtc_state->base.event //will be provided on atomic_commit complete > drm_crtc_vblank_get(crtc) > mtk_crtc->event > > > I have tried to protect this line only: > > spin_lock_irqsave(&crtc->dev->event_lock, flags); > mtk_crtc->event = mtk_crtc_state->base.event; > spin_lock_irqrestore(&crtc->dev->event_lock,flags); > > I can still see the error message "new event while there is still a > pending event" when I toggled the night light mode. > > Maybe that is mtk_crtc->event here: > if (mtk_crtc->event && mtk_crtc_state->base.event) > haven't set to NULL by mtk_drm_crtc_finish_page_flip(). > > But that not a problem because we will protect mtk_crtc->event here: > mtk_crtc->event = mtk_crtc_state->base.event; > > > So should we remove that error message since it doesn't help and may > cause the confuse after we fix this issue? > > >> I'm still able to reproduce it so I gave it a try, and this approach >> also seems to fix the issue. :) >> FWIW, the way I reproduce that is to toggle the night light mode on >> and off repeatedly through the UI panel while playing YouTube videos >> on my device. >> >> Jason, can you post a new version with Angelo's suggestion? >> > > OK, I can take Angelo's suggestion. Thanks! > But I am wondering if we should remove this log? > DRM_ERROR("new event while there is still a pending event\n"); >
Thanks for the analysis.
Please don't remove that line, this indicates that there might be another issue somewhere else, and someone will tackle that later.
Regards, Angelo
> > Regards, > Jason-JH.Lin > >> Regards, >> Fei >> >>> >>> Regards, >>> Angelo >>> >>
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