DragonFlyBSD

I operate two HAMMER arrays, each with PFSs that are mirrored via ``hammer mirror-stream`` from an array master to an array slave.

I recently upgraded to DragonFly 5.6.

After 18 hours of activity, I encountered a kernel fault that reliably can be provoked by running ``hammer mirror-stream`` on one PFS.

I've disabled PFS mirroring until this can be corrected.

Here is the transcribed error from the kernel fault:

```
panic: assertion "cursor->flags & HAMMER_CURSOR_ITERATE_CHECK" failed in hammer_btree_iterate at /usr/src/sys/vfs/hammer/hammer_btree.c:263
cpuid = 2
Trace beginning at frame 0xfffff801e6875158
hammer_btree_iterate() at hammer_btree_iterate+0x839 0xffffffff80900db9
hammer_btree_iterate() at hammer_btree_iterate+0x839 0xffffffff80900db9
hammer_mirror_delete_to.irsra.2() at hammer_mirror_delete_to.isra.2+0x12 0xffffffff80914d92
hammer_ioc_mirror_write() at hammer_ioc_mirror_write+0x3b7 0xffffffff809159a7
hammer_ioctl() at hammer_ioctl+0xebe 0xffffffff809143de
hammer_vop_ioctl() at hammer_vop_ioctl+0x48 0xffffffff8092d458
Debugger("panic")

CPU2 stopping CPUs: 0x0000000b
stopped
Stopped at Debugger+0x7c: movb $0,0xfc9be9(%rip)
db>
```

Unfortunately, nothing was saved to /var/crash for this fault except an empty ``kern.0`` file.