Re: [PATCH] drm/syncobj: use newly allocated stub fences

Sorry, I forgot to checkpatch this, I'll resend it momentarily.

-David

On Thu, Apr 8, 2021 at 6:34 PM David Stevens stevensd@chromium.org wrote:

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;
  

+};

/*

• 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...) \

2.31.0.208.g409f899ff0-goog