Btrfs: split the global ordered extents mutex

When we create a snapshot, we just need wait the ordered extents in
the source fs/file root, but because we use the global mutex to protect
this ordered extents list of the source fs/file root to avoid accessing
a empty list, if someone got the mutex to access the ordered extents list
of the other fs/file root, we had to wait.

This patch splits the above global mutex, now every fs/file root has
its own mutex to protect its own list.
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>

fs/btrfs/ctree.h

@@ -1814,6 +1814,8 @@ struct btrfs_root {
 	struct list_head delalloc_inodes;
 	struct list_head delalloc_root;
 	u64 nr_delalloc_inodes;
+
+	struct mutex ordered_extent_mutex;
 	/*
 	 * this is used by the balancing code to wait for all the pending
 	 * ordered extents

fs/btrfs/disk-io.c

@@ -1220,6 +1220,7 @@ static void __setup_root(u32 nodesize, u32 leafsize, u32 sectorsize,
 	spin_lock_init(&root->log_extents_lock[1]);
 	mutex_init(&root->objectid_mutex);
 	mutex_init(&root->log_mutex);
+	mutex_init(&root->ordered_extent_mutex);
 	init_waitqueue_head(&root->log_writer_wait);
 	init_waitqueue_head(&root->log_commit_wait[0]);
 	init_waitqueue_head(&root->log_commit_wait[1]);

fs/btrfs/ordered-data.c

@@ -595,7 +595,7 @@ static void btrfs_run_ordered_extent_work(struct btrfs_work *work)
  * wait for all the ordered extents in a root.  This is done when balancing
  * space between drives.
  */
-static int __btrfs_wait_ordered_extents(struct btrfs_root *root, int nr)
+int btrfs_wait_ordered_extents(struct btrfs_root *root, int nr)
 {
 	struct list_head splice, works;
 	struct btrfs_ordered_extent *ordered, *next;
@@ -604,6 +604,7 @@ static int __btrfs_wait_ordered_extents(struct btrfs_root *root, int nr)
 	INIT_LIST_HEAD(&splice);
 	INIT_LIST_HEAD(&works);
 
+	mutex_lock(&root->ordered_extent_mutex);
 	spin_lock(&root->ordered_extent_lock);
 	list_splice_init(&root->ordered_extents, &splice);
 	while (!list_empty(&splice) && nr) {
@@ -635,17 +636,7 @@ static int __btrfs_wait_ordered_extents(struct btrfs_root *root, int nr)
 		btrfs_put_ordered_extent(ordered);
 		cond_resched();
 	}
-
-	return count;
-}
-
-int btrfs_wait_ordered_extents(struct btrfs_root *root, int nr)
-{
-	int count;
-
-	mutex_lock(&root->fs_info->ordered_operations_mutex);
-	count = __btrfs_wait_ordered_extents(root, nr);
-	mutex_unlock(&root->fs_info->ordered_operations_mutex);
+	mutex_unlock(&root->ordered_extent_mutex);
 
 	return count;
 }
@@ -670,7 +661,7 @@ void btrfs_wait_ordered_roots(struct btrfs_fs_info *fs_info, int nr)
 			       &fs_info->ordered_roots);
 		spin_unlock(&fs_info->ordered_root_lock);
 
-		done = __btrfs_wait_ordered_extents(root, nr);
+		done = btrfs_wait_ordered_extents(root, nr);
 		btrfs_put_fs_root(root);
 
 		spin_lock(&fs_info->ordered_root_lock);