Two successive QEMU+riscv64 freebsd-vm-image runs boots to Amnesiac

[svmhdvn]

Repro (on my machine, not confirmed):

1. Run a clean build to confirm a successful run

bricoler freebsd-regression-test-suite --freebsd-src-git-checkout/url=/usr/src --freebsd-src-git-checkout/branch= --freebsd-src-build/toolchain=llvm21 --freebsd-src-build/machine=riscv/riscv64 --freebsd-vm-image/rc_kld_list= --freebsd-vm-image/packages= --freebsd-regression-test-suite/hypervisor=qemu --freebsd-regression-test-suite/tests=bin/echo --freebsd-src-build/clean=True

2. Run an incremental build without clean

bricoler freebsd-regression-test-suite --freebsd-src-git-checkout/url=/usr/src --freebsd-src-git-checkout/branch= --freebsd-src-build/toolchain=llvm21 --freebsd-src-build/machine=riscv/riscv64 --freebsd-vm-image/rc_kld_list= --freebsd-vm-image/packages= --freebsd-regression-test-suite/hypervisor=qemu --freebsd-regression-test-suite/tests=bin/echo

Observe this output:

Timecounters tick every 1.000 msec
usb_needs_explore_all: no devclass
Trying to mount root from ufs:/dev/gpt/rootfs [rw]...
sbi_ipi0: using for IPIs
Release APs
WARNING: WITNESS option enabled, expect reduced performance.
rm: /firstboot: Read-only file system

Wed Sep 23 01:01:11 UTC 2026

FreeBSD/riscv (Amnesiac) (ttyu0)

login: root
root
2026-09-23T01:01:11.748792+00:00 - login 49 - - login on ttyu0 as root
2026-09-23T01:01:11.760562+00:00 - login 49 - - ROOT LOGIN (root) ON ttyu0
Can't mkdir /var/run/xdg
2026-09-23T01:01:11.774463+00:00 - login 49 - - pam_open_session(): Session failure

This is not reproducible with the RVVM emulator.

[markjdb]

Does building with --freebsd-src-build/kernel_config=QEMU fix the problem for you?

[svmhdvn]

No, this is still reproducible with the QEMU kernconf, at least on my system.

[markjdb]

I can reproduce this too. Quite weird, clearly the mountroot code is supposed to be mounting / with the rw flag. Adding a debug print to the mountroot code temporarily fixes the problem.

[markjdb]

Can you reproduce this problem with commit 99360212c7392f2b0b3932b40f005c71e943b65f reverted in the src tree?