Re: [Linaro-mm-sig] [PATCH] drm/syncobj: use newly allocated stub fences

Am 08.04.21 um 11:34 schrieb David Stevens:

From: David Stevens stevensd@chromium.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@chromium.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...) \