question about gpg --verify

hello,

root@deviant:~-# ll
total 105M
-rw-r--r-- 1 root root 834 mars 2 13:07 linux-5.4.1.tar.sign
-rw-r--r-- 1 root root 105M nov. 29 10:17 linux-5.4.1.tar.xz
-rw-r--r-- 1 root root 40K fi(C)vr. 28 17:36 sha256sums.asc
drwxr-xr-x 2 root root 4,0K mars 2 12:33 tmp
root@deviant:~-# sha256sum linux-5.4.1.tar.xz
a7d48bb324d53e421ffbe4da40087b3c0c5112707e5f3d827c30118542c74fd9 linux-5.4.1.tar.xz
root@deviant:~-# grep `sha256sum linux-5.4.1.tar.xz |awk '{print $1}'` sha256sums.asc
a7d48bb324d53e421ffbe4da40087b3c0c5112707e5f3d827c30118542c74fd9 linux-5.4.1.tar.xz
root@deviant:~-#
root@deviant:~-#

shasum is OK ...

root@deviant:~-#
root@deviant:~-# gpg --list-keys
gpg: keyserver option 'ca-cert-file' is obsolete; please use 'hkp-cacert' in dirmngr.conf
/root/.gnupg/pubring.kbx
------------------------
pub rsa2048/0x79BE3E4300411886 2011-09-20 [SC]
Key fingerprint = ABAF 11C6 5A29 70B1 30AB E3C4 79BE 3E43 0041 1886
uid [ unknown] Linus Torvalds <torvalds@kernel.org>
uid [ unknown] Linus Torvalds <torvalds@linux-foundation.org>
sub rsa2048/0x88BCE80F012F54CA 2011-09-20 [E]

pub rsa4096/0x38DBBDC86092693E 2011-09-23 [SC]
Key fingerprint = 647F 2865 4894 E3BD 4571 99BE 38DB BDC8 6092 693E
uid [ unknown] Greg Kroah-Hartman <gregkh@linuxfoundation.org>
uid [ unknown] Greg Kroah-Hartman <gregkh@kernel.org>
uid [ unknown] Greg Kroah-Hartman (Linux kernel stable release signing key) <greg@kroah.com>
sub rsa4096/0xF38153E276D54749 2011-09-23 [E]

root@deviant:~-#
root@deviant:~-# gpg --verify linux-5.4.1.tar.sign linux-5.4.1.tar.xz
gpg: keyserver option 'ca-cert-file' is obsolete; please use 'hkp-cacert' in dirmngr.conf
gpg: Signature made ven. 29 nov. 2019 10:11:32 CET
gpg: using RSA key 647F28654894E3BD457199BE38DBBDC86092693E
gpg: BAD signature from "Greg Kroah-Hartman <gregkh@linuxfoundation.org>" [unknown]
root@deviant:~-#
root@deviant:~-#

Obviously there is something i don't understand with verification ...
Please help ...

root@deviant:~-# uname -a
Linux deviant 5.4.1 #1 SMP Mon Mar 2 11:39:11 CET 2020 x86_64 GNU/Linux
root@deviant:~-# cat /etc/*lease
PRETTY_NAME="Devuan GNU/Linux ascii"
NAME="Devuan GNU/Linux"
ID=devuan
ID_LIKE=debian
HOME_URL="https://www.devuan.org/"
SUPPORT_URL="https://devuan.org/os/community"
BUG_REPORT_URL="https://bugs.devuan.org/"
root@deviant:~-#

Thanks for your time.