[PATCH 1/4] sync_file: add a mutex to protect fence and callback members.

[Dave Airlie]

From: Dave Airlie <airlied at redhat.com>

This isn't needed currently, but to reuse sync file for Vulkan
permanent shared semaphore semantics, we need to be able to swap
the fence backing a sync file. This patch adds a mutex to the
sync file and uses to protect accesses to the fence and cb members.

Signed-off-by: Dave Airlie <airlied at redhat.com>
---
 drivers/dma-buf/sync_file.c | 23 +++++++++++++++++++----
 include/linux/sync_file.h   |  3 +++
 2 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
index 2321035..105f48c 100644
--- a/drivers/dma-buf/sync_file.c
+++ b/drivers/dma-buf/sync_file.c
@@ -47,6 +47,7 @@ static struct sync_file *sync_file_alloc(void)
 
 	INIT_LIST_HEAD(&sync_file->cb.node);
 
+	mutex_init(&sync_file->lock);
 	return sync_file;
 
 err:
@@ -204,10 +205,13 @@ static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
 	if (!sync_file)
 		return NULL;
 
+	mutex_lock(&a->lock);
+	mutex_lock(&b->lock);
 	a_fences = get_fences(a, &a_num_fences);
 	b_fences = get_fences(b, &b_num_fences);
-	if (a_num_fences > INT_MAX - b_num_fences)
-		return NULL;
+	if (a_num_fences > INT_MAX - b_num_fences) {
+		goto unlock;
+	}
 
 	num_fences = a_num_fences + b_num_fences;
 
@@ -268,11 +272,17 @@ static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
 		goto err;
 	}
 
+	mutex_unlock(&b->lock);
+	mutex_unlock(&a->lock);
+
 	strlcpy(sync_file->name, name, sizeof(sync_file->name));
 	return sync_file;
 
 err:
 	fput(sync_file->file);
+unlock:
+	mutex_unlock(&b->lock);
+	mutex_unlock(&a->lock);
 	return NULL;
 
 }
@@ -299,16 +309,20 @@ static int sync_file_release(struct inode *inode, struct file *file)
 static unsigned int sync_file_poll(struct file *file, poll_table *wait)
 {
 	struct sync_file *sync_file = file->private_data;
+	unsigned int ret_val;
 
 	poll_wait(file, &sync_file->wq, wait);
 
+	mutex_lock(&sync_file->lock);
 	if (!test_and_set_bit(POLL_ENABLED, &sync_file->fence->flags)) {
 		if (dma_fence_add_callback(sync_file->fence, &sync_file->cb,
 					   fence_check_cb_func) < 0)
 			wake_up_all(&sync_file->wq);
 	}
+	ret_val = dma_fence_is_signaled(sync_file->fence) ? POLLIN : 0;
+	mutex_unlock(&sync_file->lock);
 
-	return dma_fence_is_signaled(sync_file->fence) ? POLLIN : 0;
+	return ret_val;
 }
 
 static long sync_file_ioctl_merge(struct sync_file *sync_file,
@@ -393,6 +407,7 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
 	if (info.flags || info.pad)
 		return -EINVAL;
 
+	mutex_lock(&sync_file->lock);
 	fences = get_fences(sync_file, &num_fences);
 
 	/*
@@ -433,7 +448,7 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
 
 out:
 	kfree(fence_info);
-
+	mutex_unlock(&sync_file->lock);
 	return ret;
 }
 
diff --git a/include/linux/sync_file.h b/include/linux/sync_file.h
index 3e3ab84..5aef17f 100644
--- a/include/linux/sync_file.h
+++ b/include/linux/sync_file.h
@@ -30,6 +30,7 @@
  * @wq:			wait queue for fence signaling
  * @fence:		fence with the fences in the sync_file
  * @cb:			fence callback information
+ * @lock:               mutex to protect fence/cb - used for semaphores
  */
 struct sync_file {
 	struct file		*file;
@@ -43,6 +44,8 @@ struct sync_file {
 
 	struct dma_fence	*fence;
 	struct dma_fence_cb cb;
+	/* protects the fence pointer and cb */
+	struct mutex lock;
 };
 
 #define POLL_ENABLED DMA_FENCE_FLAG_USER_BITS
-- 
2.7.4