Hi Christian, First bad commit (maybe != root cause): tree: https://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux.git debugfs_namespaces head: 4e2b1b4274aaf7efdd1c24460febdf001421e695 commit: 738289244f9f67ce3281dfece66c6e2f728b6501 [1/4] debugfs: add ns entry reproduce: # apt-get install sparse # sparse version: v0.6.1-rc1-42-g38eda53-dirty git checkout 738289244f9f67ce3281dfece66c6e2f728b6501 make ARCH=x86_64 allmodconfig make C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' If you fix the issue, kindly add following tag Reported-by: kbuild test robot <lkp(a)intel.com&gt; sparse warnings: (new ones prefixed by >>) fs/nsfs.c:196:14: sparse: sparse: undefined identifier 'NS_GET_USERNS' fs/nsfs.c:198:14: sparse: sparse: undefined identifier 'NS_GET_PARENT' fs/nsfs.c:202:14: sparse: sparse: undefined identifier 'NS_GET_NSTYPE' fs/nsfs.c:204:14: sparse: sparse: undefined identifier 'NS_GET_OWNER_UID' fs/nsfs.c:198:14: sparse: sparse: incompatible types for 'case' statement fs/nsfs.c:202:14: sparse: sparse: incompatible types for 'case' statement fs/nsfs.c:204:14: sparse: sparse: incompatible types for 'case' statement fs/nsfs.c:19:30: sparse: sparse: symbol 'ns_file_operations' redeclared with different type (originally declared at include/linux/nsfs.h:6) - different modifiers fs/nsfs.c:244:29: sparse: sparse: undefined identifier 'debugfs_real_fops' fs/nsfs.c:196:14: sparse: sparse: Expected constant expression in case statement fs/nsfs.c:198:14: sparse: sparse: Expected constant expression in case statement fs/nsfs.c:202:14: sparse: sparse: Expected constant expression in case statement fs/nsfs.c:204:14: sparse: sparse: Expected constant expression in case statement vim +/case +196 fs/nsfs.c 6786741dbf99e44 Andrey Vagin 2016-09-06 186 6786741dbf99e44 Andrey Vagin 2016-09-06 187 static long ns_ioctl(struct file *filp, unsigned int ioctl, 6786741dbf99e44 Andrey Vagin 2016-09-06 188 unsigned long arg) 6786741dbf99e44 Andrey Vagin 2016-09-06 189 { d95fa3c76a66b6d Michael Kerrisk (man-pages 2017-01-25 190) struct user_namespace *user_ns; 6786741dbf99e44 Andrey Vagin 2016-09-06 191 struct ns_common *ns = get_proc_ns(file_inode(filp)); d95fa3c76a66b6d Michael Kerrisk (man-pages 2017-01-25 192) uid_t __user *argp; d95fa3c76a66b6d Michael Kerrisk (man-pages 2017-01-25 193) uid_t uid; 6786741dbf99e44 Andrey Vagin 2016-09-06 194 6786741dbf99e44 Andrey Vagin 2016-09-06 195 switch (ioctl) { 6786741dbf99e44 Andrey Vagin 2016-09-06 @196 case NS_GET_USERNS: 6786741dbf99e44 Andrey Vagin 2016-09-06 197 return open_related_ns(ns, ns_get_owner); a7306ed8d94af72 Andrey Vagin 2016-09-06 198 case NS_GET_PARENT: a7306ed8d94af72 Andrey Vagin 2016-09-06 199 if (!ns->ops->get_parent) a7306ed8d94af72 Andrey Vagin 2016-09-06 200 return -EINVAL; a7306ed8d94af72 Andrey Vagin 2016-09-06 201 return open_related_ns(ns, ns->ops->get_parent); e5ff5ce6e20ee22 Michael Kerrisk (man-pages 2017-01-25 202) case NS_GET_NSTYPE: e5ff5ce6e20ee22 Michael Kerrisk (man-pages 2017-01-25 203) return ns->ops->type; d95fa3c76a66b6d Michael Kerrisk (man-pages 2017-01-25 204) case NS_GET_OWNER_UID: d95fa3c76a66b6d Michael Kerrisk (man-pages 2017-01-25 205) if (ns->ops->type != CLONE_NEWUSER) d95fa3c76a66b6d Michael Kerrisk (man-pages 2017-01-25 206) return -EINVAL; d95fa3c76a66b6d Michael Kerrisk (man-pages 2017-01-25 207) user_ns = container_of(ns, struct user_namespace, ns); d95fa3c76a66b6d Michael Kerrisk (man-pages 2017-01-25 208) argp = (uid_t __user *) arg; d95fa3c76a66b6d Michael Kerrisk (man-pages 2017-01-25 209) uid = from_kuid_munged(current_user_ns(), user_ns->owner); d95fa3c76a66b6d Michael Kerrisk (man-pages 2017-01-25 210) return put_user(uid, argp); 6786741dbf99e44 Andrey Vagin 2016-09-06 211 default: 6786741dbf99e44 Andrey Vagin 2016-09-06 212 return -ENOTTY; 6786741dbf99e44 Andrey Vagin 2016-09-06 213 } 6786741dbf99e44 Andrey Vagin 2016-09-06 214 } 6786741dbf99e44 Andrey Vagin 2016-09-06 215 :::::: The code at line 196 was first introduced by commit :::::: 6786741dbf99e44fb0c0ed85a37582b8a26f1c3b nsfs: add ioctl to get an owning user namespace for ns file descriptor :::::: TO: Andrey Vagin <avagin(a)openvz.org&gt; :::::: CC: Eric W. Biederman <ebiederm(a)xmission.com&gt; --- 0-DAY kernel test infrastructure Open Source Technology Center https://lists.01.org/pipermail/kbuild-all Intel Corporation