dma-buf/sync_file: Allow multiple sync_files to wrap a single dma-fence

Up until recently sync_file were create to export a single dma-fence to
userspace, and so we could canabalise a bit insie dma-fence to mark
whether or not we had enable polling for the sync_file itself. However,
with the advent of syncobj, we do allow userspace to create multiple
sync_files for a single dma-fence. (Similarly, that the sw-sync
validation framework also started returning multiple sync-files wrapping
a single dma-fence for a syncpt also triggering the problem.)

This patch reverts my suggestion in commit e24165537312
("dma-buf/sync_file: only enable fence signalling on poll()") to use a
single bit in the shared dma-fence and restores the sync_file->flags for
tracking the bits individually.

Reported-by: Gustavo Padovan <gustavo.padovan@collabora.com>
Fixes: f1e8c67123cf ("dma-buf/sw-sync: Use an rbtree to sort fences in the timeline")
Fixes: e9083420bbac ("drm: introduce sync objects (v4)")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: Gustavo Padovan <gustavo@padovan.org>
Cc: dri-devel@lists.freedesktop.org
Cc: <drm-intel-fixes@lists.freedesktop.org> # v4.13-rc1+
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170728212951.7818-1-chris@chris-wilson.co.uk

1 files changed, 3 insertions, 2 deletions

diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
index d7e219d2669d..66fb40d0ebdb 100644
--- a/drivers/dma-buf/sync_file.c
+++ b/drivers/dma-buf/sync_file.c
@@ -304,7 +304,7 @@ static int sync_file_release(struct inode *inode, struct file *file)
 {
         struct sync_file *sync_file = file->private_data;
 
-        if (test_bit(POLL_ENABLED, &sync_file->fence->flags))
+        if (test_bit(POLL_ENABLED, &sync_file->flags))
                 dma_fence_remove_callback(sync_file->fence, &sync_file->cb);
         dma_fence_put(sync_file->fence);
         kfree(sync_file);
@@ -318,7 +318,8 @@ static unsigned int sync_file_poll(struct file *file, poll_table *wait)
 
         poll_wait(file, &sync_file->wq, wait);
 
-        if (!test_and_set_bit(POLL_ENABLED, &sync_file->fence->flags)) {
+        if (list_empty(&sync_file->cb.node) &&
+            !test_and_set_bit(POLL_ENABLED, &sync_file->flags)) {
                 if (dma_fence_add_callback(sync_file->fence, &sync_file->cb,
                                            fence_check_cb_func) < 0)
                         wake_up_all(&sync_file->wq);