f2fs: fix to avoid race when accessing last_disk_size

last_disk_size could be wrong due to concurrently updating, so using
i_sem semaphore to make last_disk_size updating exclusive to fix this
issue.
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/data.c

@@ -1570,8 +1570,11 @@ static int __write_data_page(struct page *page, bool *submitted,
 			err = do_write_data_page(&fio);
 		}
 	}
+
+	down_write(&F2FS_I(inode)->i_sem);
 	if (F2FS_I(inode)->last_disk_size < psize)
 		F2FS_I(inode)->last_disk_size = psize;
+	up_write(&F2FS_I(inode)->i_sem);
 
 done:
 	if (err && err != -ENOENT)

fs/f2fs/f2fs.h

@@ -2284,9 +2284,10 @@ static inline void clear_file(struct inode *inode, int type)
 
 static inline bool f2fs_skip_inode_update(struct inode *inode, int dsync)
 {
+	bool ret;
+
 	if (dsync) {
 		struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
-		bool ret;
 
 		spin_lock(&sbi->inode_lock[DIRTY_META]);
 		ret = list_empty(&F2FS_I(inode)->gdirty_list);
@@ -2297,7 +2298,12 @@ static inline bool f2fs_skip_inode_update(struct inode *inode, int dsync)
 			file_keep_isize(inode) ||
 			i_size_read(inode) & PAGE_MASK)
 		return false;
-	return F2FS_I(inode)->last_disk_size == i_size_read(inode);
+
+	down_read(&F2FS_I(inode)->i_sem);
+	ret = F2FS_I(inode)->last_disk_size == i_size_read(inode);
+	up_read(&F2FS_I(inode)->i_sem);
+
+	return ret;
 }
 
 static inline int f2fs_readonly(struct super_block *sb)

fs/f2fs/file.c

@@ -777,6 +777,10 @@ int f2fs_setattr(struct dentry *dentry, struct iattr *attr)
 			inode->i_mtime = inode->i_ctime = current_time(inode);
 		}
 
+		down_write(&F2FS_I(inode)->i_sem);
+		F2FS_I(inode)->last_disk_size = i_size_read(inode);
+		up_write(&F2FS_I(inode)->i_sem);
+
 		size_changed = true;
 	}