Nothing stops the hangcheck timer that submitted jobs arm, or the
job_done_work that the render-done interrupt queues, 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 the
late callbacks run on the vc4_dev embedding them after it has been
freed.

Drain them in vc4_v3d_unbind(): shut the timer down and cancel
reset_work before the interrupt is taken down, because its
vc4_irq_reset() re-enables it, then flush job_done_work so that
completions queued at teardown still release their jobs.

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 # 6.2+
Link: https://lore.kernel.org/r/20260909053509.657074-1-fanwu01@zju.edu.cn
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>
---
Changes in v2 (Maíra Canal, Sashiko review):

- Drop the VC4_GEN_4 guards: vc4_v3d_unbind() only runs on GEN4.
- State why reset_work must stop before the interrupt is taken down
  instead of describing the calls.
- Flush job_done_work instead of cancelling it, so completions queued
  at teardown still release their jobs.
- Relax the stable floor to 6.2+ now that vc4->gen is not referenced.
 drivers/gpu/drm/vc4/vc4_v3d.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/gpu/drm/vc4/vc4_v3d.c b/drivers/gpu/drm/vc4/vc4_v3d.c
index f32410420d3e..3f9f43074122 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 +498,15 @@ static void vc4_v3d_unbind(struct device *dev, struct device *master,
 	struct drm_device *drm = data;
 	struct vc4_dev *vc4 = to_vc4_dev(drm);
 
+	/* A straggler vc4_irq_reset() re-enables the interrupt. */
+	timer_shutdown_sync(&vc4->hangcheck.timer);
+	cancel_work_sync(&vc4->hangcheck.reset_work);
+
 	vc4_irq_uninstall(drm);
 
+	/* Flush rather than cancel, so queued completions release their jobs. */
+	flush_work(&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.