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

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Date:   Tue, 26 Apr 2022 14:50:43 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     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
Cc:     linux-kernel@...r.kernel.org, robdclark@...il.com,
        dmitry.baryshkov@...aro.org, dianders@...omium.org,
        quic_kalyant@...cinc.com
Subject: Re: [PATCH] drm/msm/disp/dpu1: avoid clearing hw interrupts if
 hw_intr is null during drm uninit

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.

> 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++)