segfault on loadvm after migrate_set_capability multifd on

Host environment

• Operating system: Ubuntu 24.04
• OS/kernel version: Linux 6.11.0-19-generic
• Architecture: x86_64
• QEMU flavor: qemu-system-x86_64
• QEMU version: commit 71119ed3 (and also commit 1dae461a )
• QEMU command line:

  qemu-system-x86_64 \                                                                                                                             139 ↵
   -cpu host \
   -accel kvm,dirty-ring-size=4096 \
   -m 256M \
   -drive file=artifacts/disk.qcow2,format=qcow2,if=virtio \
   -machine pc-i440fx-9.2 \
   -s\
   -monitor "tcp::4444,server,nowait" \
   -nographic

Emulated/Virtualized environment

• Operating system: Ubuntu 16.04.3 LTS
• OS/kernel version: 4.4.0-87-generic
• Architecture: x86_64

Description of problem

A segfault occurs when running loadvm having set migrate_set_capability multifd on from the monitor. EDIT: also savevm segfaults.

Steps to reproduce

1. Take a snapshot with savevm test
2. From the monitor run migrate_set_capability multifd on
3. Try to restore the snapshot with loadvm test

Additional information

Sorry for not having triaged this much, I think it is worth reporting anyway.