gpt-auto-generator fails with BTRFS root and without initramfs #16953
Description
systemd version the issue has been seen with
244, 245
Used distribution
Gentoo
Expected behaviour you didn't see
No gpt-auto-generator errors in log
Unexpected behaviour you saw
gpt-auto-generator in log
[ 0.000000] kernel: microcode: microcode updated early to revision 0xd6, date = 2020-04-23 [ 0.000000] kernel: Linux version 5.7.19-gentoo (root@host) (gcc version 9.3.0 (Gentoo 9.3.0-r1 p3), GNU ld (Gentoo 2.33.1 p2) 2.33.1) #1 SMP Sun Aug 30 19:36:07 MSK 2020 .... [ 1.675394] kernel: BTRFS: device label rootfs devid 1 transid 29806 /dev/root scanned by swapper/0 (1) [ 1.682853] kernel: BTRFS info (device nvme0n1p2): disk space caching is enabled [ 1.682854] kernel: BTRFS info (device nvme0n1p2): has skinny extents [ 1.689825] kernel: BTRFS info (device nvme0n1p2): enabling ssd optimizations [ 1.690632] kernel: VFS: Mounted root (btrfs filesystem) readonly on device 0:18. [ 1.690904] kernel: devtmpfs: mounted .... [ 1.727637] systemd[1]: systemd 245 running in system mode. (+PAM -AUDIT -SELINUX +IMA -APPARMOR +SMACK +SYSVINIT +UTMP -LIBCRYPTSETUP +GCRYPT +GNUTLS +ACL -XZ +LZ4 +SECCOMP +BLKID -ELFUTILS +KMOD +IDN2 -IDN +PCRE2 default-hierarchy=unified) .... [ 1.744141] systemd-gpt-auto-generator[288]: Disabling root partition auto-detection, root= is defined. [ 1.744161] systemd-gpt-auto-generator[288]: Failed to determine block device of root file system: No such file or directory .... [ 1.754426] systemd[280]: /lib/systemd/system-generators/systemd-gpt-auto-generator failed with exit status 1 .... [ 1.807716] BTRFS info (device nvme0n1p2): disk space caching is enabled .... [ 2.102263] systemd-remount-fs[303]: Remounting /... .... [ 2.134333] systemd[1]: Started udev Kernel Device Manager. .... [ 2.160822] systemd[1]: dev-nvme0n1.device: Changed dead -> plugged [ 2.160859] systemd[1]: sys-devices-pci0000:00-0000:00:1d.0-0000:02:00.0-nvme-nvme0-nvme0n1.device: Changed dead -> plugged [ 2.169856] kernel: BTRFS info (device nvme0n1p2): device fsid 43c77ec4-9cb8-48df-96a3-9024b881b015 devid 1 moved old:/dev/root new:/dev/nvme0n1p2 .... [ 2.168393] systemd[1]: dev-disk-by\x2dpartuuid-5c4e98cb\x2ded7f\x2d435f\x2d83a9\x2d0b78b567b4f0.device: Changed dead -> plugged [ 2.168420] systemd[1]: dev-disk-by\x2dpartuuid-5c4e98cb\x2ded7f\x2d435f\x2d83a9\x2d0b78b567b4f0.device: Job 27 dev-disk-by\x2dpartuuid-5c4e98cb\x2ded7f\x2d435f\x2d83a9\x2d0b78b567b4f0.device/start finished, result=done [ 2.168451] systemd[1]: Found device Viper M.2 VPR100 boot. [ 2.168484] systemd[1]: dev-nvme0n1p1.device: Changed dead -> plugged .... [ 2.172881] systemd[1]: dev-disk-by\x2dpartuuid-97f8aae5\x2d86b6\x2d40b5\x2d9ffb\x2d496d80551b37.device: Changed dead -> plugged [ 2.172905] systemd[1]: dev-disk-by\x2dpartuuid-97f8aae5\x2d86b6\x2d40b5\x2d9ffb\x2d496d80551b37.device: Job 22 dev-disk-by\x2dpartuuid-97f8aae5\x2d86b6\x2d40b5\x2d9ffb\x2d496d80551b37.device/start finished, result=done [ 2.172926] systemd[1]: Found device Viper M.2 VPR100 rootfs. [ 2.172951] systemd[1]: dev-disk-by\x2did-nvme\x2deui.6479a72782353833\x2dpart2.device: Changed dead -> plugged [ 2.172970] systemd[1]: dev-disk-by\x2dpath-pci\x2d0000:02:00.0\x2dnvme\x2d1\x2dpart2.device: Changed dead -> plugged [ 2.172993] systemd[1]: dev-disk-by\x2duuid-43c77ec4\x2d9cb8\x2d48df\x2d96a3\x2d9024b881b015.device: Changed dead -> plugged [ 2.173018] systemd[1]: dev-disk-by\x2dpartlabel-rootfs.device: Changed dead -> plugged [ 2.173053] systemd[1]: sys-devices-pci0000:00-0000:00:1d.0-0000:02:00.0-nvme-nvme0-nvme0n1-nvme0n1p2.device: Changed dead -> plugged [ 2.173089] systemd[1]: dev-nvme0n1p2.device: Changed tentative -> plugged Steps to reproduce the problem
0. Ensure that you have machine with UEFI and your drive is GPT-partitioned with BTRFS root partition.
- Build (obtain) kernel with drivers for your HDD/SSD compiled-in (modules will not work as you need to mount your HDD/SSD before modules are loaded).
- Create boot entry (preferably in GRUB2 loader) without initramfs and kernel command line with "root=PARTUUID=xxx-xx-xx" (substitute your PARTUUID of root partition).
- Check errors in systemd log.
I saw similar reports with "root=/dev/...", but I checked only with PARTUUID identification.
Additional information
When kernel mounts root fs without iniramfs helper, it's mounted using fake temporal mount point alias /dev/root (as real /dev is not available before root fs). After drive is re-scanned by udev mount point is properly updated (see kernel: BTRFS info (device nvme0n1p2): device fsid xxx-x-x-xxx devid 1 moved old:/dev/root new:/dev/nvme0n1p2 in log), but gpt-auto-generator already finished with error.
Old bug report: https://bugs.freedesktop.org/show_bug.cgi?id=84689
Related Linux Kernel bug report: https://bugzilla.kernel.org/show_bug.cgi?id=89721
Workaround
As a workaround, I specified all mounts (/, swap) in /etc/fstab and disabled gpt-auto-generator completely by systemd.gpt_auto=no kernel command line parameter.
It even speeds up boot process by ~100-200 msec.