Re: [PATCH v9 11/16] drm/panfrost: Move perfcnt GPU disable sequence into a helper

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [High] Use-after-free of pfdev->perfcnt in GPU interrupt handler on device unbind due to devres cleanup order.
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commit 62f6a919f812a1a1e64197b8f8a6a6d6f4790287
Author: Adrián Larumbe <adrian.larumbe@collabora.com>

drm/panfrost: Move perfcnt GPU disable sequence into a helper
    
This commit factors out the performance counter hardware disable sequence into a
new helper function panfrost_perfcnt_hw_disable() to reduce repetition.

> diff --git a/drivers/gpu/drm/panfrost/panfrost_perfcnt.c b/drivers/gpu/drm/panfrost/panfrost_perfcnt.c
> index 7020c0192e189..f71534e741b65 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_perfcnt.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_perfcnt.c
> @@ -35,6 +35,16 @@ struct panfrost_perfcnt {
>  	struct completion dump_comp;
>  };
>  
> +static void panfrost_perfcnt_hw_disable(struct panfrost_device *pfdev)
> +{
> +	gpu_write(pfdev, GPU_PERFCNT_CFG,
> +		  GPU_PERFCNT_CFG_MODE(GPU_PERFCNT_CFG_MODE_OFF));
> +	gpu_write(pfdev, GPU_PRFCNT_JM_EN, 0x0);
> +	gpu_write(pfdev, GPU_PRFCNT_SHADER_EN, 0x0);
> +	gpu_write(pfdev, GPU_PRFCNT_MMU_L2_EN, 0x0);
> +	gpu_write(pfdev, GPU_PRFCNT_TILER_EN, 0);
> +}
> +
>  void panfrost_perfcnt_clean_cache_done(struct panfrost_device *pfdev)
>  {
>  	complete(&pfdev->perfcnt->dump_comp);

[Severity: High]
This isn't a bug introduced by this patch, but can this dereference of
pfdev->perfcnt in panfrost_perfcnt_clean_cache_done() lead to a
use-after-free during device unbind?

The allocation order in panfrost_device_init() establishes a devres LIFO free
order that could cause this:

panfrost_device.c:panfrost_device_init() {
    ...
    err = panfrost_gpu_init(pfdev);
    // Registers GPU IRQ via devm_request_irq()
    ...
    err = panfrost_perfcnt_init(pfdev);
    // Allocates pfdev->perfcnt via devm_kzalloc()
    ...
}

Because devres cleans up in LIFO order, on device unbind, pfdev->perfcnt is
freed before the GPU IRQ handler is unregistered.

Additionally, panfrost_device_fini() temporarily un-suspends the device, which
unmasks the hardware interrupts via panfrost_device_reset(), and then calls
panfrost_gpu_fini(). While panfrost_gpu_fini() powers off the hardware, it
does not mask the interrupts.

If the shared IRQ line fires during this window, or if reading GPU_INT_STAT
returns 0xFFFFFFFF because power domains are off, panfrost_gpu_irq_handler()
will execute, pass the state & GPU_IRQ_CLEAN_CACHES_COMPLETED check, and call
panfrost_perfcnt_clean_cache_done().

Would this result in a use-after-free when accessing
pfdev->perfcnt->dump_comp?

[ ... ]

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Sashiko AI review · https://sashiko.dev/#/patchset/20260912-claude-fixes-v9-0-e588feaa61ef@collabora.com?part=11