Hi Peter,

[auto build test ERROR on linus/master]
[also build test ERROR on v4.8-rc5 next-20160825]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
[Suggest to use git(>=2.9.0) format-patch --base=<commit> (or --base=auto for convenience) to record what (public, well-known) commit your patch series was built on]
[Check https://git-scm.com/docs/git-format-patch for more information]

url:    https://github.com/0day-ci/linux/commits/Peter-Zijlstra/Question-on-smp_mb__before_spinlock/20160905-174026
config: i386-randconfig-s1-201636 (attached as .config)
compiler: gcc-6 (Debian 6.1.1-9) 6.1.1 20160705
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

All errors (new ones prefixed by >>):

   fs/overlayfs/readdir.c: In function 'ovl_dir_fsync':
>> fs/overlayfs/readdir.c:449:4: error: implicit declaration of function 'smp_mb__before_spinlock' [-Werror=implicit-function-declaration]
       smp_mb__before_spinlock();
       ^~~~~~~~~~~~~~~~~~~~~~~
   cc1: some warnings being treated as errors

vim +/smp_mb__before_spinlock +449 fs/overlayfs/readdir.c

d45f00ae Al Viro        2014-10-28  443  		realfile = lockless_dereference(od->upperfile);
e9be9d5e Miklos Szeredi 2014-10-24  444  		if (!realfile) {
e9be9d5e Miklos Szeredi 2014-10-24  445  			struct path upperpath;
e9be9d5e Miklos Szeredi 2014-10-24  446  
e9be9d5e Miklos Szeredi 2014-10-24  447  			ovl_path_upper(dentry, &upperpath);
e9be9d5e Miklos Szeredi 2014-10-24  448  			realfile = ovl_path_open(&upperpath, O_RDONLY);
d45f00ae Al Viro        2014-10-28 @449  			smp_mb__before_spinlock();
5955102c Al Viro        2016-01-22  450  			inode_lock(inode);
3d268c9b Al Viro        2014-10-23  451  			if (!od->upperfile) {
e9be9d5e Miklos Szeredi 2014-10-24  452  				if (IS_ERR(realfile)) {

:::::: The code at line 449 was first introduced by commit
:::::: d45f00ae43e63eff1b3d79df20610ae1ef645ebd overlayfs: barriers for opening upper-layer directory

:::::: TO: Al Viro <viro@zeniv.linux.org.uk>
:::::: CC: Al Viro <viro@zeniv.linux.org.uk>

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