linux-kernel - Re: [Freedreno] [PATCH] drm/msm/disp/dpu1: avoid clearing hw interrupts if hw

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Date:   Mon, 2 May 2022 11:05:24 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Abhinav Kumar <quic_abhinavk@...cinc.com>
Cc:     Stephen Boyd <swboyd@...omium.org>,
        Vinod Polimera <quic_vpolimer@...cinc.com>,
        devicetree@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        quic_kalyant@...cinc.com, robdclark@...il.com,
        linux-kernel@...r.kernel.org, dianders@...omium.org
Subject: Re: [Freedreno] [PATCH] drm/msm/disp/dpu1: avoid clearing hw
 interrupts if hw_intr is null during drm uninit

On Mon, 2 May 2022 at 04:38, Abhinav Kumar <quic_abhinavk@...cinc.com> wrote:
>
> Looks like our new CI has given all the answers we need :) which is a
> great win for the CI in my opinion.
>
> Take a look at this report :
> https://gitlab.freedesktop.org/drm/msm/-/jobs/22015361
>
> This issue seems to be because this change
> https://github.com/torvalds/linux/commit/169466d4e59ca204683998b7f45673ebf0eb2de6
> is missing in our tree.
>
> Without this change, what happens is that we are not hitting the return
> 0 because we check for ENODEV.
>
>
>    /*
>       * External bridges are mandatory for eDP interfaces: one has to
>       * provide at least an eDP panel (which gets wrapped into
> panel-bridge).
>       *
>       * For DisplayPort interfaces external bridges are optional, so
>       * silently ignore an error if one is not present (-ENODEV).
>       */
>      rc = dp_parser_find_next_bridge(dp_priv->parser);
>      if (!dp->is_edp && rc == -ENODEV)
>          return 0;
>
> So, I think we should do both:
>
> 1) Since we are running CI on the tree, backport this change so that
> this error path doesnt hit?
>
> 2) Add this protection as well because this shows that we can indeed hit
> this path in EDEFER cases causing this crash.

I have been waiting for v2 for the last week or so. It should include
a fixed Fixes tag and an updated description (which should note that
this happens in the error path, etc) as requested by Stephen.

>
> Thanks
>
> Abhinav
>
> On 4/27/2022 3:53 AM, Dmitry Baryshkov wrote:
> > On 27/04/2022 00:50, Stephen Boyd wrote:
> >> Quoting Vinod Polimera (2022-04-25 23:02:11)
> >>> Avoid clearing irqs and derefernce hw_intr when hw_intr is null.
> >>
> >> Presumably this is only the case when the display driver doesn't fully
> >> probe and something probe defers? Can you clarify how this situation
> >> happens?
> >>
> >>>
> >>> BUG: Unable to handle kernel NULL pointer dereference at virtual
> >>> address 0000000000000000
> >>>
> >>> Call trace:
> >>>   dpu_core_irq_uninstall+0x50/0xb0
> >>>   dpu_irq_uninstall+0x18/0x24
> >>>   msm_drm_uninit+0xd8/0x16c
> >>>   msm_drm_bind+0x580/0x5fc
> >>>   try_to_bring_up_master+0x168/0x1c0
> >>>   __component_add+0xb4/0x178
> >>>   component_add+0x1c/0x28
> >>>   dp_display_probe+0x38c/0x400
> >>>   platform_probe+0xb0/0xd0
> >>>   really_probe+0xcc/0x2c8
> >>>   __driver_probe_device+0xbc/0xe8
> >>>   driver_probe_device+0x48/0xf0
> >>>   __device_attach_driver+0xa0/0xc8
> >>>   bus_for_each_drv+0x8c/0xd8
> >>>   __device_attach+0xc4/0x150
> >>>   device_initial_probe+0x1c/0x28
> >>>
> >>> Fixes: a73033619ea ("drm/msm/dpu: squash dpu_core_irq into
> >>> dpu_hw_interrupts")
> >>
> >> The fixes tag looks odd. In dpu_core_irq_uninstall() at that commit it
> >> is dealing with 'irq_obj' which isn't a pointer. After commit
> >> f25f656608e3 ("drm/msm/dpu: merge struct dpu_irq into struct
> >> dpu_hw_intr") dpu_core_irq_uninstall() starts using 'hw_intr' which is
> >> allocated on the heap. If we backported this patch to a place that had
> >> a73033619ea without f25f656608e3 it wouldn't make any sense.
> >
> > I'd agree here. The following tag would be correct:
> >
> > Fixes: f25f656608e3 ("drm/msm/dpu: merge struct dpu_irq into struct
> > dpu_hw_intr")
> >
> >
> >>
> >>> Signed-off-by: Vinod Polimera <quic_vpolimer@...cinc.com>
> >>> ---
> >>>   drivers/gpu/drm/msm/disp/dpu1/dpu_hw_interrupts.c | 3 +++
> >>>   1 file changed, 3 insertions(+)
> >>>
> >>> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_interrupts.c
> >>> b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_interrupts.c
> >>> index c515b7c..ab28577 100644
> >>> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_interrupts.c
> >>> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_interrupts.c
> >>> @@ -599,6 +599,9 @@ void dpu_core_irq_uninstall(struct dpu_kms *dpu_kms)
> >>>   {
> >>>          int i;
> >>>
> >>> +       if (!dpu_kms->hw_intr)
> >>> +               return;
> >>> +
> >>>          pm_runtime_get_sync(&dpu_kms->pdev->dev);
> >>>          for (i = 0; i < dpu_kms->hw_intr->total_irqs; i++)
> >
> >



-- 
With best wishes
Dmitry