f2fs: avoid race in between read xattr & write xattr

Thread A:					Thread B:
-f2fs_getxattr
   -lookup_all_xattrs
      -xnid = F2FS_I(inode)->i_xattr_nid;
						-f2fs_setxattr
						    -__f2fs_setxattr
						        -write_all_xattrs
						            -truncate_xattr_node
							          ...  ...
						-write_checkpoint
								  ...  ...
						-alloc_nid   <- nid reuse
          -get_node_page
              -f2fs_bug_on  <- nid != node_footer->nid

It's need a rw_sem to avoid the race
Signed-off-by: Yunlei He <heyunlei@huawei.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/f2fs.h

@@ -589,6 +589,7 @@ struct f2fs_inode_info {
 	struct extent_tree *extent_tree;	/* cached extent_tree entry */
 	struct rw_semaphore dio_rwsem[2];/* avoid racing between dio and gc */
 	struct rw_semaphore i_mmap_sem;
+	struct rw_semaphore i_xattr_sem; /* avoid racing between reading and changing EAs */
 
 	int i_extra_isize;		/* size of extra space located in i_addr */
 	kprojid_t i_projid;		/* id for project quota */

fs/f2fs/super.c

@@ -630,6 +630,7 @@ static struct inode *f2fs_alloc_inode(struct super_block *sb)
 	init_rwsem(&fi->dio_rwsem[READ]);
 	init_rwsem(&fi->dio_rwsem[WRITE]);
 	init_rwsem(&fi->i_mmap_sem);
+	init_rwsem(&fi->i_xattr_sem);
 
 #ifdef CONFIG_QUOTA
 	memset(&fi->i_dquot, 0, sizeof(fi->i_dquot));

fs/f2fs/xattr.c

@@ -473,8 +473,10 @@ int f2fs_getxattr(struct inode *inode, int index, const char *name,
 	if (len > F2FS_NAME_LEN)
 		return -ERANGE;
 
+	down_read(&F2FS_I(inode)->i_xattr_sem);
 	error = lookup_all_xattrs(inode, ipage, index, len, name,
 				&entry, &base_addr);
+	up_read(&F2FS_I(inode)->i_xattr_sem);
 	if (error)
 		return error;
 
@@ -503,7 +505,9 @@ ssize_t f2fs_listxattr(struct dentry *dentry, char *buffer, size_t buffer_size)
 	int error = 0;
 	size_t rest = buffer_size;
 
+	down_read(&F2FS_I(inode)->i_xattr_sem);
 	error = read_all_xattrs(inode, NULL, &base_addr);
+	up_read(&F2FS_I(inode)->i_xattr_sem);
 	if (error)
 		return error;
 
@@ -686,7 +690,9 @@ int f2fs_setxattr(struct inode *inode, int index, const char *name,
 	f2fs_lock_op(sbi);
 	/* protect xattr_ver */
 	down_write(&F2FS_I(inode)->i_sem);
+	down_write(&F2FS_I(inode)->i_xattr_sem);
 	err = __f2fs_setxattr(inode, index, name, value, size, ipage, flags);
+	up_write(&F2FS_I(inode)->i_xattr_sem);
 	up_write(&F2FS_I(inode)->i_sem);
 	f2fs_unlock_op(sbi);