Re: [PATCH] drm/vc4: drain the hangcheck timer and works on V3D unbind

["Maíra Canal" <mcanal@igalia.com>]

Hi Fan Wu,

On 09/09/26 02:35, Fan Wu wrote:
> The hangcheck timer, which every submitted job arms and which queues
> reset_work once a job stops making progress, and the job_done_work,
> which the render-done interrupt queues to release completed jobs, are
> never drained at teardown: vc4_irq_disable() cancels only
> overflow_mem_work, and vc4_gem_destroy() runs from the drm-managed
> release, after vc4_v3d_unbind() has already uninstalled the V3D
> interrupt and cleared vc4->v3d.
> 
> A timer still armed by then reads V3D registers through the NULL
> vc4->v3d pointer, and late callbacks run on the vc4_dev embedding
> them after it has been freed.
> 
> Drain them in vc4_v3d_unbind(): shut the hangcheck timer down and
> cancel reset_work before the interrupt is taken down, because
> vc4_irq_reset() in a straggler reset re-enables it, then cancel
> job_done_work once no source is left, before vc4->v3d is cleared.
> 
> This issue was found by an in-house static analysis tool.
> 
> Fixes: d5b1a78a772f ("drm/vc4: Add support for drawing 3D frames.")
> Cc: stable@vger.kernel.org # 6.13+: vc4->gen does not exist on older trees
> Assisted-by: Codex:gpt-5.6
> Co-developed-by: Song Li <songl@zju.edu.cn>
> Signed-off-by: Song Li <songl@zju.edu.cn>
> Signed-off-by: Fan Wu <fanwu01@zju.edu.cn>
> ---
>   drivers/gpu/drm/vc4/vc4_v3d.c | 11 +++++++++++
>   1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/gpu/drm/vc4/vc4_v3d.c b/drivers/gpu/drm/vc4/vc4_v3d.c
> index f32410420d3e..11d4df3164b4 100644
> --- a/drivers/gpu/drm/vc4/vc4_v3d.c
> +++ b/drivers/gpu/drm/vc4/vc4_v3d.c
> @@ -9,6 +9,7 @@
>   #include <linux/component.h>
>   #include <linux/platform_device.h>
>   #include <linux/pm_runtime.h>
> +#include <linux/timer.h>
>   
>   #include <drm/drm_print.h>
>   
> @@ -497,8 +498,18 @@ static void vc4_v3d_unbind(struct device *dev, struct device *master,
>   	struct drm_device *drm = data;
>   	struct vc4_dev *vc4 = to_vc4_dev(drm);
>   
> +	/* Kill the timer, then reset_work: vc4_irq_reset() re-enables it. */

This comment provides no insight about the code, it's just describing
it.

> +	if (vc4->gen == VC4_GEN_4) {

No need for this guards, as this function only runs on VC4_GEN_4.

> +		timer_shutdown_sync(&vc4->hangcheck.timer);
> +		cancel_work_sync(&vc4->hangcheck.reset_work);
> +	}
> +
>   	vc4_irq_uninstall(drm);
>   
> +	/* Nothing can queue job_done_work any more; drain it. */
> +	if (vc4->gen == VC4_GEN_4)
> +		cancel_work_sync(&vc4->job_done_work);

Check Sashiko's feedback about this.

Best regards,
- Maíra

> +
>   	/* Disable the binner's overflow memory address, so the next
>   	 * driver probe (if any) doesn't try to reuse our old
>   	 * allocation.
>