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>

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index a84e59b7b00646b132827c709396d147a2542b04..91a8ca7af77ed65725168e20e597843bc58f6ce2 100644 (file)
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1746,6 +1746,7 @@ struct btrfs_root {
        int force_cow;
 
        spinlock_t root_item_lock;
+       atomic_t refs;
 };
 
 struct btrfs_ioctl_defrag_range_args {

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index c65a5aac1e45de711fcd4e85ceba8ea196b767b3..90b643e07f3caa8d9146019bc13f8a1988a1d066 100644 (file)
--- 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)

diff --git a/fs/btrfs/disk-io.h b/fs/btrfs/disk-io.h
index 534d583e609db9cbb4686461057d27412750d45f..b71acd6e1e5b1941e75ed4c5c056d47268cdc407 100644 (file)
--- a/fs/btrfs/disk-io.h
+++ b/fs/btrfs/disk-io.h
@@ -76,6 +76,27 @@ void btrfs_btree_balance_dirty_nodelay(struct btrfs_root *root);
 void btrfs_drop_and_free_fs_root(struct btrfs_fs_info *fs_info,
                                 struct btrfs_root *root);
 void btrfs_free_fs_root(struct btrfs_root *root);
+
+/*
+ * This function is used to grab the root, and avoid it is freed when we
+ * access it. But it doesn't ensure that the tree is not dropped.
+ *
+ * If you want to ensure the whole tree is safe, you should use
+ *     fs_info->subvol_srcu
+ */
+static inline struct btrfs_root *btrfs_grab_fs_root(struct btrfs_root *root)
+{
+       if (atomic_inc_not_zero(&root->refs))
+               return root;
+       return NULL;
+}
+
+static inline void btrfs_put_fs_root(struct btrfs_root *root)
+{
+       if (atomic_dec_and_test(&root->refs))
+               kfree(root);
+}
+
 void btrfs_mark_buffer_dirty(struct extent_buffer *buf);
 int btrfs_buffer_uptodate(struct extent_buffer *buf, u64 parent_transid,
                          int atomic);

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index c989fe602fafb47aa8e15ca3ebb4c71104c3efb9..04066c2cc7116ec8345b0ddf6e6f61539272a478 100644 (file)
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -7469,7 +7469,7 @@ int btrfs_drop_snapshot(struct btrfs_root *root,
        } else {
                free_extent_buffer(root->node);
                free_extent_buffer(root->commit_root);
-               kfree(root);
+               btrfs_put_fs_root(root);
        }
 out_end_trans:
        btrfs_end_transaction_throttle(trans, tree_root);