Upon further investigation, this problem appears to be related to the kernel version (6.1.0-9-arm64).
After booting into my new Debian 12 installation, efibootmgr hung with no output when I attempted to delete a boot entry (`sudo efibootmgr -Bb 0006`). I downloaded the Bullseye kernel deb package and downgraded to 5.10.0-23-arm64. Using the older kernel with Debian 12 allowed me to delete the boot entry with efibootmgr. After a few seconds of efibootmgr hanging with kernel 6.1.0-9-arm64, dmesg starts logging: [ 220.565406] rcu: INFO: rcu_sched detected stalls on CPUs/tasks: [ 220.571320] rcu: 31-...0: (1 GPs behind) idle=de3c/1/0x4000000000000000 softirq=453/453 fqs=2582 [ 220.580182] (detected by 28, t=5255 jiffies, g=2537, q=452 ncpus=32) [ 220.580186] Task dump for CPU 31: [ 220.580188] task:kworker/u64:5 state:R running task stack:0 pid:378 ppid:2 flags:0x0000000a [ 220.580194] Workqueue: efi_rts_wq efi_call_rts [ 220.580203] Call trace: [ 220.580204] __switch_to+0xf0/0x170 [ 220.580211] 0x0 [ 283.592504] rcu: INFO: rcu_sched detected stalls on CPUs/tasks: [ 283.598416] rcu: 31-...0: (1 GPs behind) idle=de3c/1/0x4000000000000000 softirq=453/453 fqs=10186 [ 283.607364] (detected by 18, t=21013 jiffies, g=2537, q=644 ncpus=32) [ 283.607368] Task dump for CPU 31: [ 283.607369] task:kworker/u64:5 state:R running task stack:0 pid:378 ppid:2 flags:0x0000000a [ 283.607376] Workqueue: efi_rts_wq efi_call_rts [ 283.607382] Call trace: [ 283.607383] __switch_to+0xf0/0x170 [ 283.607388] 0x0 [ 346.620541] rcu: INFO: rcu_sched detected stalls on CPUs/tasks: [ 346.626453] rcu: 31-...0: (1 GPs behind) idle=de3c/1/0x4000000000000000 softirq=453/453 fqs=16943 [ 346.635401] (detected by 22, t=36771 jiffies, g=2537, q=1673 ncpus=32) [ 346.635404] Task dump for CPU 31: [ 346.635405] task:kworker/u64:5 state:R running task stack:0 pid:378 ppid:2 flags:0x0000000a [ 346.635411] Workqueue: efi_rts_wq efi_call_rts [ 346.635417] Call trace: [ 346.635419] __switch_to+0xf0/0x170 [ 346.635424] 0x0 [ 363.463544] INFO: task khugepaged:188 blocked for more than 120 seconds. [ 363.470242] Not tainted 6.1.0-9-arm64 #1 Debian 6.1.27-1 [ 363.476069] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [ 363.483894] task:khugepaged state:D stack:0 pid:188 ppid:2 flags:0x00000008 [ 363.483901] Call trace: [ 363.483902] __switch_to+0xf0/0x170 [ 363.483909] __schedule+0x340/0x940 [ 363.483913] schedule+0x58/0xf0 [ 363.483916] schedule_timeout+0x14c/0x180 [ 363.483919] __wait_for_common+0xd4/0x254 [ 363.483922] wait_for_completion+0x28/0x3c [ 363.483926] __flush_work.isra.0+0x180/0x2dc [ 363.483931] flush_work+0x18/0x2c [ 363.483934] __lru_add_drain_all+0x1a0/0x260 [ 363.483938] lru_add_drain_all+0x1c/0x30 [ 363.483941] khugepaged+0xa4/0x9d0 [ 363.483945] kthread+0xe0/0xe4 [ 363.483948] ret_from_fork+0x10/0x20 [ 363.483986] INFO: task efibootmgr:956 blocked for more than 120 seconds. [ 363.490681] Not tainted 6.1.0-9-arm64 #1 Debian 6.1.27-1 [ 363.496510] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [ 363.504335] task:efibootmgr state:D stack:0 pid:956 ppid:955 flags:0x00000004 [ 363.504341] Call trace: [ 363.504342] __switch_to+0xf0/0x170 [ 363.504347] __schedule+0x340/0x940 [ 363.504351] schedule+0x58/0xf0 [ 363.504354] schedule_timeout+0x14c/0x180 [ 363.504357] __wait_for_common+0xd4/0x254 [ 363.504360] wait_for_completion+0x28/0x3c [ 363.504363] virt_efi_set_variable+0x134/0x1b0 [ 363.504367] efivar_set_variable_locked+0x7c/0xfc [ 363.504370] efivar_entry_delete+0x5c/0xec [efivarfs] [ 363.504380] efivarfs_unlink+0x28/0x5c [efivarfs] [ 363.504385] vfs_unlink+0x124/0x300 [ 363.504390] do_unlinkat+0x19c/0x2c0 [ 363.504393] __arm64_sys_unlinkat+0x44/0x90 [ 363.504396] invoke_syscall+0x78/0x100 [ 363.504401] el0_svc_common.constprop.0+0x4c/0xf4 [ 363.504405] do_el0_svc+0x34/0xd0 [ 363.504408] el0_svc+0x34/0xd4 [ 363.504411] el0t_64_sync_handler+0xf4/0x120 [ 363.504414] el0t_64_sync+0x18c/0x190 [ 409.648706] rcu: INFO: rcu_sched detected stalls on CPUs/tasks: [ 409.654617] rcu: 31-...0: (1 GPs behind) idle=de3c/1/0x4000000000000000 softirq=453/453 fqs=22740 [ 409.663565] (detected by 20, t=52529 jiffies, g=2537, q=1895 ncpus=32) [ 409.663568] Task dump for CPU 31: [ 409.663570] task:kworker/u64:5 state:R running task stack:0 pid:378 ppid:2 flags:0x0000000a [ 409.663576] Workqueue: efi_rts_wq efi_call_rts [ 409.663582] Call trace: [ 409.663583] __switch_to+0xf0/0x170 [ 409.663589] 0x0