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

[Fan Wu]

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@xxxxxxxxxxxxxxx # 6.13+: vc4->gen does not exist on older trees
Assisted-by: Codex:gpt-5.6
Co-developed-by: Song Li <songl@xxxxxxxxxx>
Signed-off-by: Song Li <songl@xxxxxxxxxx>
Signed-off-by: Fan Wu <fanwu01@xxxxxxxxxx>
---
 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. */
+	if (vc4->gen == 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);
+
 	/* Disable the binner's overflow memory address, so the next
 	 * driver probe (if any) doesn't try to reuse our old
 	 * allocation.