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

Daniel Vetter
2015-12-15T09:26:11Z

On Mon, Dec 14, 2015 at 05:29:55PM -0800, Dmitry Torokhov wrote:
> 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);

What exactly is the bug here? A fence with no callbacks registered any
more shouldn't have any problem. Why exactly does this blow up?

I guess I don't really understand the bug ... we do seem to remove the
callback already.

Thanks, Daniel

> + }
>
> 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
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/dri-devel

--
Daniel Vetter
Software Engineer, Intel Corporation