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Message-ID: <fcc2eecf-b32d-1758-11d2-bd130f5925cf@amd.com>
Date: Thu, 8 Apr 2021 11:41:52 +0200
From: Christian König <christian.koenig@....com>
To: David Stevens <stevensd@...omium.org>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
Maxime Ripard <mripard@...nel.org>,
Thomas Zimmermann <tzimmermann@...e.de>,
David Airlie <airlied@...ux.ie>,
Daniel Vetter <daniel@...ll.ch>,
Sumit Semwal <sumit.semwal@...aro.org>,
dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
linux-media@...r.kernel.org, linaro-mm-sig@...ts.linaro.org
Subject: Re: [PATCH] drm/syncobj: use newly allocated stub fences
Am 08.04.21 um 11:34 schrieb David Stevens:
> From: David Stevens <stevensd@...omium.org>
>
> Allocate a new private stub fence in drm_syncobj_assign_null_handle,
> instead of using a static stub fence.
>
> When userspace creates a fence with DRM_SYNCOBJ_CREATE_SIGNALED or when
> userspace signals a fence via DRM_IOCTL_SYNCOBJ_SIGNAL, the timestamp
> obtained when the fence is exported and queried with SYNC_IOC_FILE_INFO
> should match when the fence's status was changed from the perspective of
> userspace, which is during the respective ioctl.
>
> When a static stub fence started being used in by these ioctls, this
> behavior changed. Instead, the timestamp returned by SYNC_IOC_FILE_INFO
> became the first time anything used the static stub fence, which has no
> meaning to userspace.
>
> Signed-off-by: David Stevens <stevensd@...omium.org>
> ---
> drivers/dma-buf/dma-fence.c | 33 ++++++++++++++++++++++++++++++++-
> drivers/gpu/drm/drm_syncobj.c | 28 ++++++++++++++++++++--------
> include/linux/dma-fence.h | 1 +
> 3 files changed, 53 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
> index d64fc03929be..6081eb962490 100644
> --- a/drivers/dma-buf/dma-fence.c
> +++ b/drivers/dma-buf/dma-fence.c
> @@ -26,6 +26,11 @@ EXPORT_TRACEPOINT_SYMBOL(dma_fence_signaled);
> static DEFINE_SPINLOCK(dma_fence_stub_lock);
> static struct dma_fence dma_fence_stub;
>
> +struct drm_fence_private_stub {
> + struct dma_fence base;
> + spinlock_t lock;
> +};
> +
You can drop this. The spinlock is only used when the fence is signaled
to avoid races between signaling and adding a callback.
And for this the global spinlock should be perfectly sufficient. Apart
from that looks good to me.
Regards,
Christian.
> /*
> * fence context counter: each execution context should have its own
> * fence context, this allows checking if fences belong to the same
> @@ -123,7 +128,9 @@ static const struct dma_fence_ops dma_fence_stub_ops = {
> /**
> * dma_fence_get_stub - return a signaled fence
> *
> - * Return a stub fence which is already signaled.
> + * Return a stub fence which is already signaled. The fence's
> + * timestamp corresponds to the first time after boot this
> + * function is called.
> */
> struct dma_fence *dma_fence_get_stub(void)
> {
> @@ -141,6 +148,30 @@ struct dma_fence *dma_fence_get_stub(void)
> }
> EXPORT_SYMBOL(dma_fence_get_stub);
>
> +/**
> + * dma_fence_allocate_private_stub - return a private, signaled fence
> + *
> + * Return a newly allocated and signaled stub fence.
> + */
> +struct dma_fence *dma_fence_allocate_private_stub(void)
> +{
> + struct drm_fence_private_stub *fence;
> +
> + fence = kzalloc(sizeof(*fence), GFP_KERNEL);
> + if (fence == NULL)
> + return ERR_PTR(-ENOMEM);
> +
> + spin_lock_init(&fence->lock);
> + dma_fence_init(&fence->base,
> + &dma_fence_stub_ops,
> + &fence->lock,
> + 0, 0);
> + dma_fence_signal(&fence->base);
> +
> + return &fence->base;
> +}
> +EXPORT_SYMBOL(dma_fence_allocate_private_stub);
> +
> /**
> * dma_fence_context_alloc - allocate an array of fence contexts
> * @num: amount of contexts to allocate
> diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
> index 349146049849..c6125e57ae37 100644
> --- a/drivers/gpu/drm/drm_syncobj.c
> +++ b/drivers/gpu/drm/drm_syncobj.c
> @@ -350,12 +350,15 @@ EXPORT_SYMBOL(drm_syncobj_replace_fence);
> *
> * 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 dma_fence *fence = dma_fence_allocate_private_stub();
> + if (IS_ERR(fence))
> + return PTR_ERR(fence);
>
> - drm_syncobj_replace_fence(syncobj, fence);
> - dma_fence_put(fence);
> + drm_syncobj_replace_fence(syncobj, fence);
> + dma_fence_put(fence);
> + return 0;
> }
>
> /* 5s default for wait submission */
> @@ -469,6 +472,7 @@ 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 +483,13 @@ 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 +1331,11 @@ 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);
>
> diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
> index 9f12efaaa93a..6ffb4b2c6371 100644
> --- a/include/linux/dma-fence.h
> +++ b/include/linux/dma-fence.h
> @@ -587,6 +587,7 @@ static inline signed long dma_fence_wait(struct dma_fence *fence, bool intr)
> }
>
> struct dma_fence *dma_fence_get_stub(void);
> +struct dma_fence *dma_fence_allocate_private_stub(void);
> u64 dma_fence_context_alloc(unsigned num);
>
> #define DMA_FENCE_TRACE(f, fmt, args...) \
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