# DF-3237 verification

Kernel: DragonFly dfbsd 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026 root@dfbsd:/usr/obj/usr/src/sys/X86_64_GENERIC x86_64

## Bottom line

Speculative and not dynamically exercised: after nfssvc_iod_stop1 the reader can still requeue an EINPROGRESS (server TRYLATER) request onto nm_reqtxq whose only consumer is exiting, and nfssvc_iod_writer_wakeup is a no-op once txstate leaves WAITING - stranding a nfsreq + nfsm_info + bio (biodone never called, buffer stuck B_BUSY) whose queue head lives inside the nfsmount that nfs_unmount then frees. The window is sub-millisecond inside an umount -f racing async I/O against a JUKEBOX server; constructing that NFS topology exceeded this batch budget. Fix (drain reqtxq when the writer is dead) authored as a structural sketch in fix.diff and compile-validated in its minimal form.

## Kernel references
- sys/vfs/nfs/nfs_iod.c:134-137
- sys/vfs/nfs/nfs_iod.c:180-181
- sys/vfs/nfs/nfs_iod.c:244-247

## Exploit chain
(none: availability/correctness finding; no privilege chain)

## Fix

drain nm_reqtxq once the writer thread is STOPPING/DONE

See fix.diff in this directory (git-apply-able against the read-only sys/
tree; applied only inside the disposable verification guest).

## Reproduction

build: n/a

run: n/a (umount -f vs JUKEBOX server race)

expected: n/a

## Notes on the PoC (what changed vs the finding sketch)

(none)

## Fix status (batch validation)
Applied with the 36 sibling fix.diffs of this batch in findings/poc/_batch41/all_fixes.patch; single in-guest `make -j6 nativekernel KERNCONF=X86_64_GENERIC` completed RC=0 with zero errors under -Werror (full log: findings/poc/_batch41/fix_build8.log). Behavior A/B intentionally skipped for this Info-tier item.