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Subject[PATCH v4 5/5] dma-buf/sync_file: only enable fence signalling on poll()
Date
From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>

Signalling doesn't need to be enabled at sync_file creation, it is only
required if userspace waiting the fence to signal through poll().

Thus we delay fence_add_callback() until poll is called. It only adds the
callback the first time poll() is called. This avoid re-adding the same
callback multiple times.

v2: rebase and update to work with new fence support for sync_file

v3: use atomic operation to set enabled and protect fence_add_callback()

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
---
drivers/dma-buf/sync_file.c | 22 +++++++++++++---------
include/linux/sync_file.h | 2 ++
2 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
index 61a687c..240ef22 100644
--- a/drivers/dma-buf/sync_file.c
+++ b/drivers/dma-buf/sync_file.c
@@ -86,8 +86,6 @@ struct sync_file *sync_file_create(struct fence *fence)
fence->ops->get_timeline_name(fence), fence->context,
fence->seqno);

- fence_add_callback(fence, &sync_file->cb, fence_check_cb_func);
-
return sync_file;
}
EXPORT_SYMBOL(sync_file_create);
@@ -269,9 +267,6 @@ static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
goto err;
}

- fence_add_callback(sync_file->fence, &sync_file->cb,
- fence_check_cb_func);
-
strlcpy(sync_file->name, name, sizeof(sync_file->name));
return sync_file;

@@ -286,7 +281,8 @@ static void sync_file_free(struct kref *kref)
struct sync_file *sync_file = container_of(kref, struct sync_file,
kref);

- fence_remove_callback(sync_file->fence, &sync_file->cb);
+ if (atomic_read(&sync_file->enabled))
+ fence_remove_callback(sync_file->fence, &sync_file->cb);
fence_put(sync_file->fence);
kfree(sync_file);
}
@@ -306,13 +302,21 @@ static unsigned int sync_file_poll(struct file *file, poll_table *wait)

poll_wait(file, &sync_file->wq, wait);

+ if (!atomic_xchg(&sync_file->enabled, 1)) {
+ if (fence_add_callback(sync_file->fence, &sync_file->cb,
+ fence_check_cb_func) < 0)
+ wake_up_all(&sync_file->wq);
+ }
+
status = fence_is_signaled(sync_file->fence);

- if (status)
- return POLLIN;
+ if (!status)
+ return 0;
+
if (status < 0)
return POLLERR;
- return 0;
+
+ return POLLIN;
}

static long sync_file_ioctl_merge(struct sync_file *sync_file,
diff --git a/include/linux/sync_file.h b/include/linux/sync_file.h
index f7de5a0..4ced13b 100644
--- a/include/linux/sync_file.h
+++ b/include/linux/sync_file.h
@@ -28,6 +28,7 @@
* @name: name of sync_file. Useful for debugging
* @sync_file_list: membership in global file list
* @wq: wait queue for fence signaling
+ * @enabled: wether fence signal is enabled or not
* @fence: fence with the fences in the sync_file
* @cb: fence callback information
*/
@@ -40,6 +41,7 @@ struct sync_file {
#endif

wait_queue_head_t wq;
+ atomic_t enabled;

struct fence *fence;
struct fence_cb cb;
--
2.5.5
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