BACKPORT: 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>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170728212951.7818-1-chris@chris-wilson.co.uk
[astrachan: rediffed against changed context lines in 4.9]
Bug: 79383895
PD#170298 [1/3]
Change-Id: I70d1f19796c6cb33cd4c19e40276d7298aa4ba5d
Signed-off-by: Alistair Strachan <astrachan@google.com>

diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
index 56a45cd..267546a 100644 (file)
--- a/drivers/dma-buf/sync_file.c
+++ b/drivers/dma-buf/sync_file.c
@@ -278,7 +278,7 @@ static void sync_file_free(struct kref *kref)
        struct sync_file *sync_file = container_of(kref, struct sync_file,
                                                     kref);
 
-       if (test_bit(POLL_ENABLED, &sync_file->fence->flags))
+       if (test_bit(POLL_ENABLED, &sync_file->flags))
                fence_remove_callback(sync_file->fence, &sync_file->cb);
        fence_put(sync_file->fence);
        kfree(sync_file);
@@ -298,7 +298,8 @@ 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 (fence_add_callback(sync_file->fence, &sync_file->cb,
                                           fence_check_cb_func) < 0)
                        wake_up_all(&sync_file->wq);

diff --git a/include/linux/sync_file.h b/include/linux/sync_file.h
index aa17ccf..35ec6c4 100644 (file)
--- a/include/linux/sync_file.h
+++ b/include/linux/sync_file.h
@@ -40,12 +40,13 @@ struct sync_file {
 #endif
 
        wait_queue_head_t       wq;
+       unsigned long           flags;
 
        struct fence            *fence;
        struct fence_cb cb;
 };
 
-#define POLL_ENABLED FENCE_FLAG_USER_BITS
+#define POLL_ENABLED 0
 
 struct sync_file *sync_file_create(struct fence *fence);
 struct fence *sync_file_get_fence(int fd);