ppc64le: `/usr/lib/grub/powerpc-ieee1275/prep-bootdev` hangs during upgrade

[Paul Menzel]

Doing `apt upgrade`

    2021-02-08 10:41:20 upgrade grub-ieee1275:ppc64el 2.04-1ubuntu26 2.04-1ubuntu26.8

the postinst hangs:

```
root 236284 0.0 0.0 18304 9536 ? S 09:59 0:00 sudo apt full-upgrade
root 236285 0.0 0.0 77376 64256 ? S 09:59 0:04 \_ apt full-upgrade
root 253209 0.0 0.0 21440 14336 pts/1 Ss+ 11:10 0:04 \_ /usr/bin/dpkg --status-fd 45 --configure --pending
root 305396 0.0 0.0 33408 24896 pts/1 S+ 11:19 0:00 \_ /usr/bin/perl -w /usr/share/debconf/frontend /var/lib/dpkg/info/grub-ieee1275.postinst configure 2.04-1ubuntu26
root 305407 0.0 0.0 12032 5632 pts/1 S+ 11:19 0:00 \_ /bin/bash /var/lib/dpkg/info/grub-ieee1275.postinst configure 2.04-1ubuntu26
root 305520 0.0 0.0 8960 3328 pts/1 D+ 11:19 0:00 \_ /usr/lib/grub/powerpc-ieee1275/prep-bootdev
```

Trying to debug a little `sudo /usr/lib/grub/powerpc-ieee1275/prep-bootdev -l` hangs too. strace shows, that it hangs when opening the non-existing `/dev/sdf`:

```
$ lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
loop1 7:1 0 65.3M 1 loop /snap/lxd/19012
loop2 7:2 0 54M 1 loop /snap/core18/1987
loop3 7:3 0 91.1M 1 loop /snap/core/10582
loop4 7:4 0 54M 1 loop /snap/core18/1946
loop5 7:5 0 91.1M 1 loop /snap/core/10575
loop6 7:6 0 65.3M 1 loop /snap/lxd/19163
sda 8:0 1 931.5G 0 disk
├─sda1 8:1 1 7M 0 part
└─sda2 8:2 1 931.5G 0 part /var/lib/docker/btrfs
sdb 8:16 1 931.5G 0 disk /amd/flughafenberlinbrandenburgwillybrandt/0
sr0 11:0 1 1024M 0 rom
sr1 11:1 1 1024M 0 rom
sr2 11:2 1 1024M 0 rom
sr3 11:3 1 1024M 0 rom
$ sudo strace -ff /usr/lib/grub/powerpc-ieee1275/prep-bootdev -l
[…]
lstat("/dev", {st_mode=S_IFDIR|0755, st_size=4920, ...}) = 0
lstat("/dev/sdc", {st_mode=S_IFBLK|0660, st_rdev=makedev(0x8, 0x20), ...}) = 0
stat("/dev/sdc", {st_mode=S_IFBLK|0660, st_rdev=makedev(0x8, 0x20), ...}) = 0
openat(AT_FDCWD, "/dev/sdc", O_RDONLY) = -1 ENOMEDIUM (No medium found)
openat(AT_FDCWD, "/dev/sdc", O_RDONLY) = -1 ENOMEDIUM (No medium found)
lstat("/dev", {st_mode=S_IFDIR|0755, st_size=4920, ...}) = 0
lstat("/dev/sdd", {st_mode=S_IFBLK|0660, st_rdev=makedev(0x8, 0x30), ...}) = 0
stat("/dev/sdd", {st_mode=S_IFBLK|0660, st_rdev=makedev(0x8, 0x30), ...}) = 0
openat(AT_FDCWD, "/dev/sdd", O_RDONLY) = -1 ENOMEDIUM (No medium found)
openat(AT_FDCWD, "/dev/sdd", O_RDONLY) = -1 ENOMEDIUM (No medium found)
lstat("/dev", {st_mode=S_IFDIR|0755, st_size=4920, ...}) = 0
lstat("/dev/sde", {st_mode=S_IFBLK|0660, st_rdev=makedev(0x8, 0x40), ...}) = 0
stat("/dev/sde", {st_mode=S_IFBLK|0660, st_rdev=makedev(0x8, 0x40), ...}) = 0
openat(AT_FDCWD, "/dev/sde", O_RDONLY) = -1 ENOMEDIUM (No medium found)
openat(AT_FDCWD, "/dev/sde", O_RDONLY) = -1 ENOMEDIUM (No medium found)
lstat("/dev", {st_mode=S_IFDIR|0755, st_size=4920, ...}) = 0
lstat("/dev/sdf", {st_mode=S_IFBLK|0660, st_rdev=makedev(0x8, 0x50), ...}) = 0
stat("/dev/sdf", {st_mode=S_IFBLK|0660, st_rdev=makedev(0x8, 0x50), ...}) = 0
openat(AT_FDCWD, "/dev/sdf", O_RDONLY
```

```
$ sudo fdisk -l
Disk /dev/loop1: 65.28 MiB, 68444160 bytes, 133680 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk /dev/loop2: 54.4 MiB, 56668160 bytes, 110680 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk /dev/loop3: 91.6 MiB, 95477760 bytes, 186480 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk /dev/loop4: 53.99 MiB, 56590336 bytes, 110528 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk /dev/loop5: 91.6 MiB, 95477760 bytes, 186480 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk /dev/loop6: 65.29 MiB, 68456448 bytes, 133704 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk /dev/sda: 931.53 GiB, 1000204886016 bytes, 1953525168 sectors
Disk model: ST1000NX0313
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: 242ACBC1-F70A-4E15-91B8-8340D055F79B

Device Start End Sectors Size Type
/dev/sda1 2048 16383 14336 7M PowerPC PReP boot
/dev/sda2 16384 1953523711 1953507328 931.5G Linux filesystem

Disk /dev/sdb: 931.53 GiB, 1000204886016 bytes, 1953525168 sectors
Disk model: ST1000NX0313
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes

```