I spoke too soon; the boot continued after almost 45 minutes, and I was able to vagrant ssh after that. I changed the timeout to 3600 and tried vagrant reload. This time it took just over 3 minutes. The kernel messages indicate “detected stall” on one vCPU, and later on, “soft lockup” on both vCPUs:
[ 4.248957] sd 2:0:0:0: [sda] Attached SCSI disk
[ 4.250353] sd 2:0:1:0: [sdb] Attached SCSI disk
[ 138.108221] rcu: INFO: rcu_sched detected stalls on CPUs/tasks:
[ 138.108404] raid6: sse2x4 gen() 41795998 MB/s
[ 138.118148] rcu: 1-…!: (2 ticks this GP) idle=e82/1/0x4000000000000000 softirq=903/906 fqs=1
[ 138.136074] (detected by 0, t=33120 jiffies, g=-567, q=238)
[ 138.146128] Sending NMI from CPU 0 to CPUs 1:
[ 148.119490] rcu: rcu_sched kthread starved for 33118 jiffies! g-567 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 ->cpu=0
[ 148.127342] rcu: RCU grace-period kthread stack dump:
[ 148.131620] rcu_sched I 0 10 2 0x80004000
[ 148.135496] Call Trace:
[ 148.137437] __schedule+0x2e3/0x740
[ 148.140070] schedule+0x42/0xb0
[ 148.142939] schedule_timeout+0x8a/0x160
[ 148.146478] ? __next_timer_interrupt+0xe0/0xe0
[ 148.149843] rcu_gp_kthread+0x48d/0x990
[ 148.153831] kthread+0x104/0x140
[ 148.157339] ? kfree_call_rcu+0x20/0x20
[ 148.161646] ? kthread_park+0x90/0x90
[ 148.165707] ret_from_fork+0x1f/0x40
[ 188.776650] watchdog: BUG: soft lockup - CPU#1 stuck for 44s! [modprobe:217]
[ 188.776631] watchdog: BUG: soft lockup - CPU#0 stuck for 38s! [swapper/0:0]
[ 188.776633] Modules linked in: raid6_pq(+) libcrc32c raid1 raid0 multipath linear mptspi scsi_transport_spi mptscsih psmouse mptbase e1000
[ 188.785353] Modules linked in: raid6_pq(+) libcrc32c raid1 raid0 multipath linear mptspi scsi_transport_spi mptscsih psmouse mptbase e1000
[ 188.794121] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.4.0-88-generic #99-Ubuntu
[ 188.817004] CPU: 1 PID: 217 Comm: modprobe Not tainted 5.4.0-88-generic #99-Ubuntu
[ 188.839315] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006
[ 188.839326] RIP: 0010:native_safe_halt+0xe/0x10
[ 188.839331] Code: 7b ff ff ff eb bd 90 90 90 90 90 90 e9 07 00 00 00 0f 00 2d 36 87 52 00 f4 c3 66 90 e9 07 00 00 00 0f 00 2d 26 87 52 00 fb f4 90 0f 1f 44 00 00 55 48 89 e5 41 55 41 54 53 e8 0d 83 63 ff 65
[ 188.852916] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006
[ 188.865108] RSP: 0018:ffffffff9dc03e18 EFLAGS: 00010246 ORIG_RAX: ffffffffffffff13
[ 188.879272] RIP: 0010:raid6_sse24_xor_syndrome+0x255/0x280 [raid6_pq]
[ 188.888449] RAX: ffffffff9d0e2c00 RBX: 0000000000000000 RCX: 0000000000000001
[ 188.907828] Code: f8 66 41 0f ef 30 66 44 0f ef 27 4d 01 f9 66 45 0f ef 31 66 0f e7 22 66 41 0f e7 30 66 44 0f e7 27 66 45 0f e7 31 83 45 d4 40 <48> 63 55 d4 48 3b 55 c0 0f 82 09 fe ff ff 0f ae f8 e8 05 08 25 dc
[ 188.920221] RDX: 0000000000001bd6 RSI: ffffffff9dc03dd8 RDI: 0000002257860dd3
[ 188.934220] RSP: 0018:ffffc2218024bb28 EFLAGS: 00010206 ORIG_RAX: ffffffffffffff13