Date: Fri, 15 May 2026 19:21:37 +0000 From: bugzilla-noreply@freebsd.org To: bugs@FreeBSD.org Subject: [Bug 295313] RB_REROOT fails with already-imported ZFS pool (regression from 15.0) Message-ID: <bug-295313-227@https.bugs.freebsd.org/bugzilla/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=295313 Bug ID: 295313 Summary: RB_REROOT fails with already-imported ZFS pool (regression from 15.0) Product: Base System Version: 15.1-STABLE Hardware: amd64 OS: Any Status: New Severity: Affects Only Me Priority: --- Component: kern Assignee: bugs@FreeBSD.org Reporter: shantanna@hotmail.com ## Summary `reboot(RB_REROOT)` panics the kernel when the target ZFS pool is already imported at the time of the call. This is a regression from FreeBSD 15.0, where the same flow worked correctly. Affects bare-metal and VM deployments equally. ## Environment - FreeBSD 15.1-STABLE (stable/15-n283579-49937a6face3), GENERIC, amd64 - GELI-encrypted ZFS root (AES-XTS-256) - Boot chain: initramfs → GELI attach remotely → zpool import → reroot ## Steps to reproduce 1. Boot any minimal FreeBSD environment (initramfs, rescue, mfsBSD) 2. Import a ZFS pool without mounting: `zpool import -f -N zroot` 3. Mount the root dataset temporarily: `mount -t zfs zroot/ROOT/default /mnt` 4. Set kernel environment: `kenv vfs.root.mountfrom="zfs:zroot/ROOT/default"` 5. Execute: `reboot(RB_REROOT)` 6. Kernel panics ## Expected Kernel unmounts the current root, mounts `zroot/ROOT/default` at `/`, starts init from the new root. Clean reroot without full reboot. GELI devices survive (GEOM classes persist across reroot). ## Actual Kernel panics in `vfs_mountroot()`. The ZFS root dataset is already mounted at `/mnt` (step 3). ZFS returns EBUSY because the dataset cannot be mounted at two locations simultaneously. ## What we tested | Pool state before reroot | Result | |--------------------------|--------| | Imported, dataset mounted at /mnt | Panic (EBUSY) | | Imported, dataset unmounted | Panic | | Exported entirely | Panic (kernel cannot re-import without GELI re-attach) | All variants panic. The pool state does not matter. ## Workaround Execute `chroot /mnt /sbin/init` from PID 1 instead of reroot. Works reliably but has side effects (nullfs deadlocks between datasets, `mount` shows `/mnt/` paths). ## Suggested fix During `RB_REROOT`, `vfs_mountroot()` should handle already-imported ZFS pools by either: a) unmounting the dataset from its current location before mounting at `/`, or b) moving the existing mount point ## Related - FreeBSD commit 4453ec5 (Dec 2025): `reboot -r` behavior change - OpenZFS issue #18542 (same bug, ZFS-side perspective) -- You are receiving this mail because: You are the assignee for the bug.home | help
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