Subject: Re: NMI stack overflow during resume of PCIe bridge with CONFIG_HARDLOCKUP_DETECTOR=y

From: Thomas Gleixner <[email-masked]>
Date: Tue, 13 Jan 2026 16:24:46 +0100

On Tue, Jan 13 2026 at 10:41, Bert Karwatzki wrote:
> Here's the result in case of the crash:
> 2026-01-12T04:24:36.809904+01:00 T1510;acpi_ex_system_memory_space_handler 255: logical_addr_ptr = ffffc066977b3000
> 2026-01-12T04:24:36.846170+01:00 C14;exc_nmi: 0

Here the NMI triggers in non-task context on CPU14

> 2026-01-12T04:24:36.960760+01:00 C14;exc_nmi: 10.3
> 2026-01-12T04:24:36.960760+01:00 C14;default_do_nmi 
> 2026-01-12T04:24:36.960760+01:00 C14;nmi_handle: type=0x0
> 2026-01-12T04:24:36.960760+01:00 C14;nmi_handle: a=0xffffffffa1612de0
> 2026-01-12T04:24:36.960760+01:00 C14;nmi_handle: a->handler=perf_event_nmi_handler+0x0/0xa6
> 2026-01-12T04:24:36.960760+01:00 C14;perf_event_nmi_handler: 0
> 2026-01-12T04:24:36.960760+01:00 C14;perf_event_nmi_handler: 1
> 2026-01-12T04:24:36.960760+01:00 C14;perf_event_nmi_handler: 2
> 2026-01-12T04:24:36.960760+01:00 C14;x86_pmu_handle_irq: 2
> 2026-01-12T04:24:36.960760+01:00 C14;x86_pmu_handle_irq: 2.6
> 2026-01-12T04:24:36.960760+01:00 C14;__perf_event_overflow: 0
> 2026-01-12T04:24:36.960760+01:00 C14;__perf_event_overflow: 6.99: overflow_handler=watchdog_overflow_callback+0x0/0x10d
> 2026-01-12T04:24:36.960760+01:00 C14;watchdog_overflow_callback: 0
> 2026-01-12T04:24:36.960760+01:00 C14;__ktime_get_fast_ns_debug: 0.1
> 2026-01-12T04:24:36.960760+01:00 C14;tk_clock_read_debug: read=read_hpet+0x0/0xf0
> 2026-01-12T04:24:36.960760+01:00 C14;read_hpet: 0
> 2026-01-12T04:24:36.960760+01:00 C14;read_hpet: 0.1

> 2026-01-12T04:24:36.960760+01:00 T0;exc_nmi: 0

This one triggers in task context of PID0, aka idle task, but it's not
clear on which CPU that happens. It's probably CPU13 as that continues
with the expected 10.3 output, but that's almost ~1.71 seconds later.

> 2026-01-12T04:24:38.674625+01:00 C13;exc_nmi: 10.3
> 2026-01-12T04:24:38.674625+01:00 C13;default_do_nmi 
> 2026-01-12T04:24:38.674625+01:00 C13;nmi_handle: type=0x0
> 2026-01-12T04:24:38.674625+01:00 C13;nmi_handle: a=0xffffffffa1612de0
> 2026-01-12T04:24:38.674625+01:00 C13;nmi_handle: a->handler=perf_event_nmi_handler+0x0/0xa6
> 2026-01-12T04:24:38.674625+01:00 C13;perf_event_nmi_handler: 0
> 2026-01-12T04:24:38.674625+01:00 C13;perf_event_nmi_handler: 1
> 2026-01-12T04:24:38.674625+01:00 C13;perf_event_nmi_handler: 2
> 2026-01-12T04:24:38.674625+01:00 C13;x86_pmu_handle_irq: 2
> 2026-01-12T04:24:38.674625+01:00 C13;x86_pmu_handle_irq: 2.6
> 2026-01-12T04:24:38.674625+01:00 C13;__perf_event_overflow: 0
> 2026-01-12T04:24:38.674625+01:00 C13;__perf_event_overflow: 6.99: overflow_handler=watchdog_overflow_callback+0x0/0x10d
> 2026-01-12T04:24:38.674625+01:00 C13;watchdog_overflow_callback: 0
> 2026-01-12T04:24:38.674625+01:00 C13;__ktime_get_fast_ns_debug: 0.1
> 2026-01-12T04:24:38.674625+01:00 C13;tk_clock_read_debug: read=read_hpet+0x0/0xf0
> 2026-01-12T04:24:38.674625+01:00 C13;read_hpet: 0
> 2026-01-12T04:24:38.674625+01:00 C13;read_hpet: 0.1

> 2026-01-12T04:24:38.674625+01:00 T0;exc_nmi: 0

Same picture as above, but this time on CPU2 with a delay of 0.68
seconds

> 2026-01-12T04:24:39.355101+01:00 C2;exc_nmi: 10.3
> 2026-01-12T04:24:39.355101+01:00 C2;default_do_nmi 
> 2026-01-12T04:24:39.355101+01:00 C2;nmi_handle: type=0x0
> 2026-01-12T04:24:39.355101+01:00 C2;nmi_handle: a=0xffffffffa1612de0
> 2026-01-12T04:24:39.355101+01:00 C2;nmi_handle: a->handler=perf_event_nmi_handler+0x0/0xa6
> 2026-01-12T04:24:39.355101+01:00 C2;perf_event_nmi_handler: 0
> 2026-01-12T04:24:39.355101+01:00 C2;perf_event_nmi_handler: 1
> 2026-01-12T04:24:39.355101+01:00 C2;perf_event_nmi_handler: 2
> 2026-01-12T04:24:39.355101+01:00 C2;x86_pmu_handle_irq: 2
> 2026-01-12T04:24:39.355101+01:00 C2;x86_pmu_handle_irq: 2.6
> 2026-01-12T04:24:39.355101+01:00 C2;__perf_event_overflow: 0
> 2026-01-12T04:24:39.355101+01:00 C2;__perf_event_overflow: 6.99: overflow_handler=watchdog_overflow_callback+0x0/0x10d
> 2026-01-12T04:24:39.355101+01:00 C2;watchdog_overflow_callback: 0
> 2026-01-12T04:24:39.355101+01:00 C2;__ktime_get_fast_ns_debug: 0.1
> 2026-01-12T04:24:39.355101+01:00 C2;tk_clock_read_debug: read=read_hpet+0x0/0xf0
> 2026-01-12T04:24:39.355101+01:00 C2;read_hpet: 0
> 2026-01-12T04:24:39.355101+01:00 C2;read_hpet: 0.1

> 2026-01-12T04:24:39.355101+01:00 T0;exc_nmi: 0

Again on CPU0 with a delay of 0.06 seconds

> 2026-01-12T04:24:39.410207+01:00 C0;exc_nmi: 10.3
> 2026-01-12T04:24:39.410207+01:00 C0;default_do_nmi 
> 2026-01-12T04:24:39.410207+01:00 C0;nmi_handle: type=0x0
> 2026-01-12T04:24:39.410207+01:00 C0;nmi_handle: a=0xffffffffa1612de0
> 2026-01-12T04:24:39.410207+01:00 C0;nmi_handle: a->handler=perf_event_nmi_handler+0x0/0xa6
> 2026-01-12T04:24:39.410207+01:00 C0;perf_event_nmi_handler: 0
> 2026-01-12T04:24:39.410207+01:00 C0;perf_event_nmi_handler: 1
> 2026-01-12T04:24:39.410207+01:00 C0;perf_event_nmi_handler: 2
> 2026-01-12T04:24:39.410207+01:00 C0;x86_pmu_handle_irq: 2
> 2026-01-12T04:24:39.410207+01:00 C0;x86_pmu_handle_irq: 2.6
> 2026-01-12T04:24:39.410207+01:00 C0;__perf_event_overflow: 0
> 2026-01-12T04:24:39.410207+01:00 C0;__perf_event_overflow: 6.99: overflow_handler=watchdog_overflow_callback+0x0/0x10d
> 2026-01-12T04:24:39.410207+01:00 C0;watchdog_overflow_callback: 0
> 2026-01-12T04:24:39.410207+01:00 C0;__ktime_get_fast_ns_debug: 0.1
> 2026-01-12T04:24:39.410207+01:00 C0;tk_clock_read_debug: read=read_hpet+0x0/0xf0
> 2026-01-12T04:24:39.410207+01:00 C0;read_hpet: 0
> 2026-01-12T04:24:39.410207+01:00 C0;read_hpet: 0.1

> 2026-01-12T04:24:39.410207+01:00 T0;exc_nmi: 0

....

> In the case of the crash the interrupt handler never returns because when accessing
> the HPET another NMI is triggered. This goes on until a crash happens, probably because
> of stack overflow.

No. NMI nesting is only one level deep and immediately returns:

        if (this_cpu_read(nmi_state) != NMI_NOT_RUNNING) {
		this_cpu_write(nmi_state, NMI_LATCHED);
		return;
	}

So it's not a stack overflow. What's more likely is that after a while
_ALL_ CPUs are hung up in the NMI handler after they tripped over the
HPET read.

> The behaviour described here seems to be similar to the bug that commit
> 3d5f4f15b778 ("watchdog: skip checks when panic is in progress") is fixing, but
> this is actually a different bug as kernel 6.18 (which contains 3d5f4f15b778)
> is also affected (I've conducted 5 tests with 6.18 so far and got 4 crashes (crashes occured
> after (0.5h, 1h, 4.5h, 1.5h) of testing)). 
> Nevertheless these look similar enough to CC the involved people.

There is nothing similar.

Your problem originates from a screwed up hardware state which in turn
causes the HPET to go haywire for unknown reasons.

What is the physical address of this ACPI handler access:

       logical_addr_ptr = ffffc066977b3000

along with the full output of /proc/iomem

Thanks,

        tglx