Btrfs: introduce grab/put functions for the root of the fs/file tree

The grab/put funtions will be used in the next patch, which need grab
the root object and ensure it is not freed. We use reference counter
instead of the srcu lock is to aovid blocking the memory reclaim task,
which invokes synchronize_srcu().

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>

1 files changed, 3 insertions, 2 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index c65a5aac1e45..90b643e07f3c 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1216,6 +1216,7 @@ static void __setup_root(u32 nodesize, u32 leafsize, u32 sectorsize,
         atomic_set(&root->log_writers, 0);
         atomic_set(&root->log_batch, 0);
         atomic_set(&root->orphan_inodes, 0);
+        atomic_set(&root->refs, 1);
         root->log_transid = 0;
         root->last_log_commit = 0;
         extent_io_tree_init(&root->dirty_log_pages,
@@ -2052,7 +2053,7 @@ static void del_fs_roots(struct btrfs_fs_info *fs_info)
                 } else {
                         free_extent_buffer(gang[0]->node);
                         free_extent_buffer(gang[0]->commit_root);
-                        kfree(gang[0]);
+                        btrfs_put_fs_root(gang[0]);
                 }
         }
 
@@ -3417,7 +3418,7 @@ static void free_fs_root(struct btrfs_root *root)
         kfree(root->free_ino_ctl);
         kfree(root->free_ino_pinned);
         kfree(root->name);
-        kfree(root);
+        btrfs_put_fs_root(root);
 }
 
 void btrfs_free_fs_root(struct btrfs_root *root)