Dear Maintainer,

after installation of intel-microcode 3.20250512.1~deb11u1 on a Dell T5600 with
dual Intel Xeon E5-2660 the system becomes totally unbootable on kernel
6.1.0-0.deb11.21-amd64:

``
0.921425] Kernel panic - not syncing: UFS: Unable to mount root fs on unknown-
block(0,0)
0.921462] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.1.0-0.deb11.21-amd64 #1
Debian 6.1.90-1~bpo11+1
0.921495] Hardware name: Dell Inc. Precision T5600/XXXXX, BIOS A19 06/30/2019
0.921521] Call Trace:
0.921535] <TASK>
0.921547] dump_stack_lvl+0x45/0x5e
0.921573] panic+0x10c/0x2b6
0.921593] mount_block_root+0x1c6/0x1d9
0.921616] prepare_namespace+0x136/0x165
0.921633] kernel_init_freeable+0x25d/0x287
0.921651] ? rest_init+0xd0/0xd0
0.921669] kernel_init+0x16/0x130
0.921685] ret_from_fork+0x22/0x30
0.921705] </TASK>
0.921790] Kernel Offset: 0x4e00000 from Oxffffffff81000000 (relocation range:
0xffffffff80000000-0xfffffffffffffff)
0.921827] ---[ end Kernel panic - not syncing: UFS: Unable to mount root fs on
unknown-block(0,0) ]---
``

On kernel 6.1.0-0.deb11.17-amd64 and intel-microcode 3.20250512.1~deb11u1 the
system is kind of bootable but shows severe errors.

A roll back to intel-microcode 3.20250211.1~deb11u1 fixes the problem for
kernel 6.1.0-0.deb11.17-amd64 and 6.1.0-0.deb11.21-amd64.

T5600 with
kernel
unknown-


https://askubuntu.com/questions/41930/kernel-panic-not-syncing-vfs-unable-to-mount-root-fs-on-unknown-block0-0
and https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=906584 clues at a
missing initramfs.
Do you have enough free space in /boot (is /boot is a separate
partition?)
What is the outcome of update-initramfs with the offending microcode
and kernel? (no need to boot).
Also you could try to load the kernel and initramfs with qemu to test
if they are correct after update-initramfs.

Unable to mount root fs means that the / partition could not be
mounted, likely because the drivers to do so are in the initramfs and
either the initramfs failed to generate.

to create a missing initramfs
update-initramfs -c -k <kernel_version>

to update an initramfs
update-initramfs -u -k <kernel_version>

though it seems unlikely to be a space issue as 3.20250211.1 is around
9MB while 3.20250512.1~deb11u1is around 11MB it could be the old kernel
initramfs plus the new one overflow the partition size.

But it is also very unlikely that a CPU bug would always fails at the
mount root fs step.

Also have you tried 3.20250512.1~deb12u1? (note the deb12u1 instead of
deb11u1 in your report)
amd64 #1
06/30/2019
(relocation range:
root fs on
3.20250512.1~deb11u1 the
for
security'), (500,
LANGUAGE not


Cheers,
Alban