linux-kernel - [PATCH 1/2] drm/vc4: Account for interrupts in flight

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Date:   Fri, 10 Nov 2017 02:05:06 +0100
From:   Stefan Schake <stschake@...il.com>
To:     dri-devel@...ts.freedesktop.org
Cc:     linux-rpi-kernel@...ts.infradead.org,
        Stefan Schake <stschake@...il.com>,
        Eric Anholt <eric@...olt.net>, David Airlie <airlied@...ux.ie>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] drm/vc4: Account for interrupts in flight

Synchronously disable the IRQ to make the following cancel_work_sync
invocation effective.

An interrupt in flight could enqueue further overflow mem work. As we
free the binner BO immediately following vc4_irq_uninstall this caused
a NULL pointer dereference in the work callback vc4_overflow_mem_work.

Link: https://github.com/anholt/linux/issues/114
Signed-off-by: Stefan Schake <stschake@...il.com>
Fixes: d5b1a78a772f ("drm/vc4: Add support for drawing 3D frames.")
---
 drivers/gpu/drm/vc4/vc4_irq.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/vc4/vc4_irq.c b/drivers/gpu/drm/vc4/vc4_irq.c
index 7d7af3a..61b2e53 100644
--- a/drivers/gpu/drm/vc4/vc4_irq.c
+++ b/drivers/gpu/drm/vc4/vc4_irq.c
@@ -208,6 +208,9 @@
 {
 	struct vc4_dev *vc4 = to_vc4_dev(dev);
 
+	/* Undo the effects of a previous vc4_irq_uninstall. */
+	enable_irq(dev->irq);
+
 	/* Enable both the render done and out of memory interrupts. */
 	V3D_WRITE(V3D_INTENA, V3D_DRIVER_IRQS);
 
@@ -225,6 +228,9 @@
 	/* Clear any pending interrupts we might have left. */
 	V3D_WRITE(V3D_INTCTL, V3D_DRIVER_IRQS);
 
+	/* Finish any interrupt handler still in flight. */
+	disable_irq(dev->irq);
+
 	cancel_work_sync(&vc4->overflow_mem_work);
 }
 
-- 
1.9.1