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SubjectRe: [PATCH] Revert "drm/syncobj: use dma_fence_get_stub"
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Am 08.04.21 um 06:59 schrieb David Stevens:
> From: David Stevens <stevensd@chromium.org>
>
> This reverts commit 86bbd89d5da66fe760049ad3f04adc407ec0c4d6.
>
> Using the singleton stub fence in drm_syncobj_assign_null_handle means
> that all syncobjs created in an already signaled state or any syncobjs
> signaled by userspace will reference the singleton fence when exported
> to a sync_file. If those sync_files are queried with SYNC_IOC_FILE_INFO,
> then the timestamp_ns value returned will correspond to whenever the
> singleton stub fence was first initialized. This can break the ability
> of userspace to use timestamps of these fences, as the singleton stub
> fence's timestamp bears no relationship to any meaningful event.

And why exactly is having the timestamp of the call to
drm_syncobj_assign_null_handle() better?

Additional if you really need that please don't revert the patch.
Instead provide a function which returns a newly initialized stub fence
in the dma_fence.c code.

Regards,
Christian.

>
> Signed-off-by: David Stevens <stevensd@chromium.org>
> ---
> drivers/gpu/drm/drm_syncobj.c | 58 ++++++++++++++++++++++++++---------
> 1 file changed, 44 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
> index 349146049849..7cc11f1a83f4 100644
> --- a/drivers/gpu/drm/drm_syncobj.c
> +++ b/drivers/gpu/drm/drm_syncobj.c
> @@ -211,6 +211,21 @@ struct syncobj_wait_entry {
> static void syncobj_wait_syncobj_func(struct drm_syncobj *syncobj,
> struct syncobj_wait_entry *wait);
>
> +struct drm_syncobj_stub_fence {
> + struct dma_fence base;
> + spinlock_t lock;
> +};
> +
> +static const char *drm_syncobj_stub_fence_get_name(struct dma_fence *fence)
> +{
> + return "syncobjstub";
> +}
> +
> +static const struct dma_fence_ops drm_syncobj_stub_fence_ops = {
> + .get_driver_name = drm_syncobj_stub_fence_get_name,
> + .get_timeline_name = drm_syncobj_stub_fence_get_name,
> +};
> +
> /**
> * drm_syncobj_find - lookup and reference a sync object.
> * @file_private: drm file private pointer
> @@ -344,18 +359,24 @@ void drm_syncobj_replace_fence(struct drm_syncobj *syncobj,
> }
> EXPORT_SYMBOL(drm_syncobj_replace_fence);
>
> -/**
> - * drm_syncobj_assign_null_handle - assign a stub fence to the sync object
> - * @syncobj: sync object to assign the fence on
> - *
> - * Assign a already signaled stub fence to the sync object.
> - */
> -static void drm_syncobj_assign_null_handle(struct drm_syncobj *syncobj)
> +static int drm_syncobj_assign_null_handle(struct drm_syncobj *syncobj)
> {
> - struct dma_fence *fence = dma_fence_get_stub();
> + struct drm_syncobj_stub_fence *fence;
>
> - drm_syncobj_replace_fence(syncobj, fence);
> - dma_fence_put(fence);
> + fence = kzalloc(sizeof(*fence), GFP_KERNEL);
> + if (fence == NULL)
> + return -ENOMEM;
> +
> + spin_lock_init(&fence->lock);
> + dma_fence_init(&fence->base, &drm_syncobj_stub_fence_ops,
> + &fence->lock, 0, 0);
> + dma_fence_signal(&fence->base);
> +
> + drm_syncobj_replace_fence(syncobj, &fence->base);
> +
> + dma_fence_put(&fence->base);
> +
> + return 0;
> }
>
> /* 5s default for wait submission */
> @@ -469,6 +490,7 @@ EXPORT_SYMBOL(drm_syncobj_free);
> int drm_syncobj_create(struct drm_syncobj **out_syncobj, uint32_t flags,
> struct dma_fence *fence)
> {
> + int ret;
> struct drm_syncobj *syncobj;
>
> syncobj = kzalloc(sizeof(struct drm_syncobj), GFP_KERNEL);
> @@ -479,8 +501,13 @@ int drm_syncobj_create(struct drm_syncobj **out_syncobj, uint32_t flags,
> INIT_LIST_HEAD(&syncobj->cb_list);
> spin_lock_init(&syncobj->lock);
>
> - if (flags & DRM_SYNCOBJ_CREATE_SIGNALED)
> - drm_syncobj_assign_null_handle(syncobj);
> + if (flags & DRM_SYNCOBJ_CREATE_SIGNALED) {
> + ret = drm_syncobj_assign_null_handle(syncobj);
> + if (ret < 0) {
> + drm_syncobj_put(syncobj);
> + return ret;
> + }
> + }
>
> if (fence)
> drm_syncobj_replace_fence(syncobj, fence);
> @@ -1322,8 +1349,11 @@ drm_syncobj_signal_ioctl(struct drm_device *dev, void *data,
> if (ret < 0)
> return ret;
>
> - for (i = 0; i < args->count_handles; i++)
> - drm_syncobj_assign_null_handle(syncobjs[i]);
> + for (i = 0; i < args->count_handles; i++) {
> + ret = drm_syncobj_assign_null_handle(syncobjs[i]);
> + if (ret < 0)
> + break;
> + }
>
> drm_syncobj_array_free(syncobjs, args->count_handles);
>

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