Weird: cant't patch debian-sources with aufs4 (other kernels can)

[patty.yivi]

After emerging debian-sources, preparing them with 'make modules_prepare' etc, then trying to emerge aufs4.

However weird error pops up:

y linux # make oldconfig
scripts/kconfig/conf  --oldconfig Kconfig
*
* Restart config...
*
*
* Hardening features (from Grsecurity)
*
Hardening features (from Grsecurity) (GRKERNSEC) [N/y/?] (NEW)
#
# configuration written to .config
#
y linux # make modules_prepare
scripts/kconfig/conf  --silentoldconfig Kconfig
  CHK     include/config/kernel.release
  CHK     include/generated/uapi/linux/version.h
  CHK     include/generated/utsrelease.h
  CHK     include/generated/package.h
  CC      kernel/bounds.s
  CHK     include/generated/bounds.h
  UPD     include/generated/bounds.h
  CHK     include/generated/timeconst.h
  UPD     include/generated/timeconst.h
  CC      arch/x86/kernel/asm-offsets.s
  CHK     include/generated/asm-offsets.h
  UPD     include/generated/asm-offsets.h
  CALL    scripts/checksyscalls.sh
  CC      scripts/mod/empty.o
  MKELF   scripts/mod/elfconfig.h
  HOSTCC  scripts/mod/modpost.o
  CC      scripts/mod/devicetable-offsets.s
  GEN     scripts/mod/devicetable-offsets.h
  HOSTCC  scripts/mod/file2alias.o
  HOSTCC  scripts/mod/sumversion.o
  HOSTLD  scripts/mod/modpost
y linux # emerge -v aufs4

 * IMPORTANT: 29 news items need reading for repository 'gentoo'.
 * Use eselect news read to view new items.


These are the packages that would be merged, in order:

Calculating dependencies... done!
[ebuild   R   ~] sys-fs/aufs4-0_pre20160223::gentoo  USE="kernel-patch -debug -doc -fuse -hfs -inotify -nfs -pax_kernel -ramfs" 0 KiB

Total: 1 package (1 reinstall), Size of downloads: 0 KiB


>>> Verifying ebuild manifests

>>> Emerging (1 of 1) sys-fs/aufs4-0_pre20160223::gentoo
 * aufs4-standalone-0_pre20160223.tar.xz SHA256 SHA512 WHIRLPOOL size ;-) ...                                                          [ ok ]
 * Determining the location of the kernel source code
 * Found kernel source directory:
 *     /usr/src/linux
 * Found sources for kernel version:
 *     4.5.2-1
 * Checking for suitable kernel configuration options...                                                                               [ ok ]
>>> Unpacking aufs4-standalone-0_pre20160223.tar.xz to /mnt/_var_tmp/_var/portage/sys-fs/aufs4-0_pre20160223/temp
 * Using origin/aufs4.x-rcN as patch source
 * Patching your kernel...
 * Applying aufs4-standalone-base-mmap-combined.patch ...

 * Failed Patch: aufs4-standalone-base-mmap-combined.patch !
 *  ( /mnt/_var_tmp/_var/portage/sys-fs/aufs4-0_pre20160223/temp/aufs4-standalone/aufs4-standalone-base-mmap-combined.patch )
 *
 * Include in your bugreport the contents of:
 *
 *   /mnt/_var_tmp/_var/portage/sys-fs/aufs4-0_pre20160223/temp/aufs4-standalone-base-mmap-combined.patch.out

 * ERROR: sys-fs/aufs4-0_pre20160223::gentoo failed (setup phase):
 *   Failed Patch: aufs4-standalone-base-mmap-combined.patch!
 *
 * Call stack:
 *                    ebuild.sh, line 133:  Called pkg_setup
 *   aufs4-0_pre20160223.ebuild, line 104:  Called epatch '/mnt/_var_tmp/_var/portage/sys-fs/aufs4-0_pre20160223/temp/aufs4-standalone/aufs4-standalone-base-mmap-combined.patch'
 *                eutils.eclass, line 612:  Called die
 * The specific snippet of code:
 *               die "Failed Patch: ${patchname}!"
 *
 * If you need support, post the output of `emerge --info '=sys-fs/aufs4-0_pre20160223::gentoo'`,
 * the complete build log and the output of `emerge -pqv '=sys-fs/aufs4-0_pre20160223::gentoo'`.
 * The complete build log is located at '/mnt/_var_tmp/_var/portage/sys-fs/aufs4-0_pre20160223/temp/build.log'.
 * The ebuild environment file is located at '/mnt/_var_tmp/_var/portage/sys-fs/aufs4-0_pre20160223/temp/die.env'.
 * Working directory: '/usr/src/linux'
 * S: '/mnt/_var_tmp/_var/portage/sys-fs/aufs4-0_pre20160223/work/aufs4-standalone'

>>> Failed to emerge sys-fs/aufs4-0_pre20160223, Log file:

>>>  '/mnt/_var_tmp/_var/portage/sys-fs/aufs4-0_pre20160223/temp/build.log'

 * Messages for package sys-fs/aufs4-0_pre20160223:

 * Patching your kernel...
 

The error holds only for debian-sources, for instance aufs4 emerges over vanilla-sources without any problem, compiles then and is running now smoothly ;)

 

BTW, why do you regard debian-sources as the best?