[PATCH] f2fs: protect free nid operation with cp_rwsem

[Chao Yu <yuchao0@huawei.com>]

- f2fs_balance_fs_bg
 - build_free_nids
  - __build_free_nids
   - scan_nat_page
    - add_free_nid
					- f2fs_create
					 - f2fs_new_inode
					  - alloc_nid
   - remove_free_nid

This patch uses cp_rwsem to protect free nid allocation/initialization
to avoid reusing allocated nid in above scenario.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
---
 fs/f2fs/inode.c   | 2 ++
 fs/f2fs/segment.c | 5 ++++-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
index 2520fa72b23f..f941410f994a 100644
--- a/fs/f2fs/inode.c
+++ b/fs/f2fs/inode.c
@@ -423,7 +423,9 @@ void f2fs_evict_inode(struct inode *inode)
 			add_ino_entry(sbi, inode->i_ino, UPDATE_INO);
 	}
 	if (is_inode_flag_set(inode, FI_FREE_NID)) {
+		f2fs_lock_op(sbi);
 		alloc_nid_failed(sbi, inode->i_ino);
+		f2fs_unlock_op(sbi);
 		clear_inode_flag(inode, FI_FREE_NID);
 	}
 	f2fs_bug_on(sbi, err &&
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 0bf024f62330..f85e1f443c99 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -426,8 +426,11 @@ void f2fs_balance_fs_bg(struct f2fs_sb_info *sbi)
 
 	if (!available_free_memory(sbi, FREE_NIDS))
 		try_to_free_nids(sbi, MAX_FREE_NIDS);
-	else
+	else {
+		f2fs_lock_op(sbi);
 		build_free_nids(sbi, false, false);
+		f2fs_unlock_op(sbi);
+	}
 
 	if (!is_idle(sbi))
 		return;
-- 
2.8.2.295.g3f1c1d0