[PATCH] android: fix warning when releasing active sync point

[Dmitry Torokhov <dtor@chromium.org>]

Userspace can close the sync device while there are still active fence
points, in which case kernel produces the following warning:

[   43.853176] ------------[ cut here ]------------
[   43.857834] WARNING: CPU: 0 PID: 892 at /mnt/host/source/src/third_party/kernel/v3.18/drivers/staging/android/sync.c:439 android_fence_release+0x88/0x104()
[   43.871741] CPU: 0 PID: 892 Comm: Binder_5 Tainted: G     U 3.18.0-07661-g0550ce9 #1
[   43.880176] Hardware name: Google Tegra210 Smaug Rev 1+ (DT)
[   43.885834] Call trace:
[   43.888294] [<ffffffc000207464>] dump_backtrace+0x0/0x10c
[   43.893697] [<ffffffc000207580>] show_stack+0x10/0x1c
[   43.898756] [<ffffffc000ab1258>] dump_stack+0x74/0xb8
[   43.903814] [<ffffffc00021d414>] warn_slowpath_common+0x84/0xb0
[   43.909736] [<ffffffc00021d530>] warn_slowpath_null+0x14/0x20
[   43.915482] [<ffffffc00088aefc>] android_fence_release+0x84/0x104
[   43.921582] [<ffffffc000671cc4>] fence_release+0x104/0x134
[   43.927066] [<ffffffc00088b0cc>] sync_fence_free+0x74/0x9c
[   43.932552] [<ffffffc00088b128>] sync_fence_release+0x34/0x48
[   43.938304] [<ffffffc000317bbc>] __fput+0x100/0x1b8
[   43.943185] [<ffffffc000317cc8>] ____fput+0x8/0x14
[   43.947982] [<ffffffc000237f38>] task_work_run+0xb0/0xe4
[   43.953297] [<ffffffc000207074>] do_notify_resume+0x44/0x5c
[   43.958867] ---[ end trace 5a2aa4027cc5d171 ]---

Let's fix it by introducing a new optional callback (disable_signaling)
to fence operations so that drivers can do proper clean ups when we
remove last callback for given fence.

Reviewed-by: Andrew Bresticker <abrestic@chromium.org>
Signed-off-by: Dmitry Torokhov <dtor@chromium.org>
---
 drivers/dma-buf/fence.c        | 6 +++++-
 drivers/staging/android/sync.c | 8 ++++++++
 include/linux/fence.h          | 2 ++
 3 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/dma-buf/fence.c b/drivers/dma-buf/fence.c
index 7b05dbe..0ed73ad 100644
--- a/drivers/dma-buf/fence.c
+++ b/drivers/dma-buf/fence.c
@@ -304,8 +304,12 @@ fence_remove_callback(struct fence *fence, struct fence_cb *cb)
 	spin_lock_irqsave(fence->lock, flags);
 
 	ret = !list_empty(&cb->node);
-	if (ret)
+	if (ret) {
 		list_del_init(&cb->node);
+		if (list_empty(&fence->cb_list))
+			if (fence->ops->disable_signaling)
+				fence->ops->disable_signaling(fence);
+	}
 
 	spin_unlock_irqrestore(fence->lock, flags);
 
diff --git a/drivers/staging/android/sync.c b/drivers/staging/android/sync.c
index e0c1acb..f8566c1 100644
--- a/drivers/staging/android/sync.c
+++ b/drivers/staging/android/sync.c
@@ -465,6 +465,13 @@ static bool android_fence_enable_signaling(struct fence *fence)
 	return true;
 }
 
+static void android_fence_disable_signaling(struct fence *fence)
+{
+	struct sync_pt *pt = container_of(fence, struct sync_pt, base);
+
+	list_del_init(&pt->active_list);
+}
+
 static int android_fence_fill_driver_data(struct fence *fence,
 					  void *data, int size)
 {
@@ -508,6 +515,7 @@ static const struct fence_ops android_fence_ops = {
 	.get_driver_name = android_fence_get_driver_name,
 	.get_timeline_name = android_fence_get_timeline_name,
 	.enable_signaling = android_fence_enable_signaling,
+	.disable_signaling = android_fence_disable_signaling,
 	.signaled = android_fence_signaled,
 	.wait = fence_default_wait,
 	.release = android_fence_release,
diff --git a/include/linux/fence.h b/include/linux/fence.h
index bb52201..ce44348 100644
--- a/include/linux/fence.h
+++ b/include/linux/fence.h
@@ -107,6 +107,7 @@ struct fence_cb {
  * @get_driver_name: returns the driver name.
  * @get_timeline_name: return the name of the context this fence belongs to.
  * @enable_signaling: enable software signaling of fence.
+ * @disable_signaling: disable software signaling of fence (optional).
  * @signaled: [optional] peek whether the fence is signaled, can be null.
  * @wait: custom wait implementation, or fence_default_wait.
  * @release: [optional] called on destruction of fence, can be null
@@ -166,6 +167,7 @@ struct fence_ops {
 	const char * (*get_driver_name)(struct fence *fence);
 	const char * (*get_timeline_name)(struct fence *fence);
 	bool (*enable_signaling)(struct fence *fence);
+	void (*disable_signaling)(struct fence *fence);
 	bool (*signaled)(struct fence *fence);
 	signed long (*wait)(struct fence *fence, bool intr, signed long timeout);
 	void (*release)(struct fence *fence);
-- 
2.6.0.rc2.230.g3dd15c0


-- 
Dmitry