I encountered a hard lockup while attempting to reproduce the panic issue that occurred on our production servers [0]. The hard lockup manifests as follows: [15852778.150191] livepatch: klp_try_switch_task: grpc_executor:421106 is sleeping on function do_exit [15852778.169471] livepatch: klp_try_switch_task: grpc_executor:421244 is sleeping on function do_exit [15852778.188746] livepatch: klp_try_switch_task: grpc_executor:421457 is sleeping on function do_exit [15852778.208021] livepatch: klp_try_switch_task: grpc_executor:422407 is sleeping on function do_exit [15852778.227292] livepatch: klp_try_switch_task: grpc_executor:423184 is sleeping on function do_exit [15852778.246576] livepatch: klp_try_switch_task: grpc_executor:423582 is sleeping on function do_exit [15852778.265863] livepatch: klp_try_switch_task: grpc_executor:423738 is sleeping on function do_exit [15852778.285149] livepatch: klp_try_switch_task: grpc_executor:423739 is sleeping on function do_exit [15852778.304446] livepatch: klp_try_switch_task: grpc_executor:423833 is sleeping on function do_exit [15852778.323738] livepatch: klp_try_switch_task: grpc_executor:423893 is sleeping on function do_exit [15852778.343017] livepatch: klp_try_switch_task: grpc_executor:423894 is sleeping on function do_exit [15852778.362292] livepatch: klp_try_switch_task: grpc_executor:423976 is sleeping on function do_exit [15852778.381565] livepatch: klp_try_switch_task: grpc_executor:423977 is sleeping on function do_exit [15852778.400847] livepatch: klp_try_switch_task: grpc_executor:424610 is sleeping on function do_exit [15852778.412319] NMI watchdog: Watchdog detected hard LOCKUP on cpu 15 ... [15852778.412374] CPU: 15 PID: 1 Comm: systemd Kdump: loaded Tainted: G S W O K 6.1.52-3 [15852778.412377] Hardware name: New H3C Technologies Co., Ltd. H3C UniServer R4950 G5/RS45M2C9S, BIOS 5.12 10/15/2021 [15852778.412378] RIP: 0010:queued_write_lock_slowpath+0x75/0x135 ... [15852778.412397] Call Trace: [15852778.412398] <NMI> [15852778.412400] ? show_regs.cold+0x1a/0x1f [15852778.412403] ? watchdog_overflow_callback.cold+0x1e/0x70 [15852778.412406] ? __perf_event_overflow+0x102/0x1e0 [15852778.412409] ? perf_event_overflow+0x19/0x20 [15852778.412411] ? x86_pmu_handle_irq+0xf7/0x160 [15852778.412415] ? flush_tlb_one_kernel+0xe/0x30 [15852778.412418] ? __set_pte_vaddr+0x2d/0x40 [15852778.412421] ? set_pte_vaddr_p4d+0x3d/0x50 [15852778.412423] ? set_pte_vaddr+0x6d/0xa0 [15852778.412424] ? __native_set_fixmap+0x28/0x40 [15852778.412426] ? native_set_fixmap+0x54/0x60 [15852778.412428] ? ghes_copy_tofrom_phys+0x75/0x120 [15852778.412431] ? __ghes_peek_estatus.isra.0+0x4e/0xb0 [15852778.412434] ? ghes_in_nmi_queue_one_entry.constprop.0+0x3d/0x240 [15852778.412437] ? amd_pmu_handle_irq+0x48/0xc0 [15852778.412438] ? perf_event_nmi_handler+0x2d/0x50 [15852778.412440] ? nmi_handle+0x60/0x120 [15852778.412443] ? default_do_nmi+0x45/0x120 [15852778.412446] ? exc_nmi+0x118/0x150 [15852778.412447] ? end_repeat_nmi+0x16/0x67 [15852778.412450] ? copy_process+0xf01/0x19f0 [15852778.412452] ? queued_write_lock_slowpath+0x75/0x135 [15852778.412455] ? queued_write_lock_slowpath+0x75/0x135 [15852778.412457] ? queued_write_lock_slowpath+0x75/0x135 [15852778.412459] </NMI> [15852778.412460] <TASK> [15852778.412461] _raw_write_lock_irq+0x43/0x50 [15852778.412463] copy_process+0xf01/0x19f0 [15852778.412466] kernel_clone+0x9d/0x3e0 [15852778.412468] ? autofs_dev_ioctl_requester+0x100/0x100 [15852778.412471] __do_sys_clone+0x66/0x90 [15852778.412475] __x64_sys_clone+0x25/0x30 [15852778.412477] do_syscall_64+0x38/0x90 [15852778.412478] entry_SYSCALL_64_after_hwframe+0x64/0xce [15852778.412481] RIP: 0033:0x7f426bb3b9c1 ... Notably, dynamic_debug is enabled to collect debug information when applying a livepatch, resulting in a large amount of debug output. The issue arises because klp_try_switch_task() holds the tasklist_lock, and if another task attempts to acquire it, it must spin until it's available. This becomes problematic in the copy_process() path, where IRQs are disabled, leading to the hard lockup. To prevent this, we should implement a check for spinlock contention before proceeding. Link: https://lore.kernel.org/live-patching/CALOAHbA9WHPjeZKUcUkwULagQjTMfqAdAg+akqPzbZ7Byc=qrw@xxxxxxxxxxxxxx/ [0] Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx> --- kernel/livepatch/transition.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c index ba069459c101..774017825bb4 100644 --- a/kernel/livepatch/transition.c +++ b/kernel/livepatch/transition.c @@ -467,9 +467,14 @@ void klp_try_complete_transition(void) * unless the patch includes changes to a very common function. */ read_lock(&tasklist_lock); - for_each_process_thread(g, task) + for_each_process_thread(g, task) { if (!klp_try_switch_task(task)) complete = false; + if (rwlock_is_contended(&tasklist_lock) || need_resched()) { + complete = false; + break; + } + } read_unlock(&tasklist_lock); /* -- 2.43.5
