Re: kdump kernel randomly hang with tick_periodic call trace on bare metal system

[Thomas Gleixner <tglx@linutronix.de>]

On Tue, Dec 20 2022 at 13:41, Baoquan He wrote:
> On one intel bare metal system, I can randomly reproduce the kdump hang
> as below with tick_periodic call trace. Attach the kernel config for
> reference.

This has absolutely nothing to do with x2apic IPI shorthands

> [    0.045980] Spurious LAPIC timer interrupt on cpu 0

So here the CPU receives a spurious Local APIC timer interrupt, but
that's a red herring.

> [    1.152690] BUG: kernel NULL pointer dereference, address: 0000000000000088
> [    1.159634] #PF: supervisor read access in kernel mode
> [    1.164757] #PF: error_code(0x0000) - not-present page
> [    1.169882] PGD 0 P4D 0 
> [    1.172407] Oops: 0000 [#1] PREEMPT SMP PTI
> [    1.176578] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 6.0.11-300.fc37.x86_64 #1
> [    1.183870] Hardware name: Dell Inc. PowerEdge R410/0N051F, BIOS 1.11.0 07/20/2012
> [    1.191420] RIP: 0010:tick_periodic+0x23/0x80

I'm willing to bet that this is caused by the following line in tick_periodic():

    update_process_times(user_mode(get_irq_regs()));

       user_mode() is invoked with a NULL pointer. user_mode() accesses
       regs->cs. CS is at offset 0x88....

The reason for this is here:

> [    1.280648]  tick_handle_periodic+0x1f/0x70
> [    1.284821]  timer_interrupt+0x14/0x20
> [    1.288561]  __handle_irq_event_percpu+0x46/0x190
> [    1.293253]  handle_irq_event+0x34/0x70
> [    1.297080]  handle_level_irq+0xa8/0x180
> [    1.300993]  resend_irqs+0x5d/0x70
> [    1.304386]  tasklet_action_common.constprop.0+0xab/0xe0
> [    1.309686]  __do_softirq+0xfb/0x319
> [    1.313254]  __irq_exit_rcu+0xd7/0x140
> [    1.316993]  common_interrupt+0xb9/0xd0

For some reason the timer interrupt is resent in software. I assume it is
the HPET interrupt because that's what just got initialized.

> [    1.143537] clocksource: hpet: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 133484882848 ns

and the callchain below just confirms that:

> [    1.393315]  _raw_spin_unlock_irqrestore+0x19/0x40
> [    1.398093]  __setup_irq+0x443/0x6d0
> [    1.401659]  request_threaded_irq+0x109/0x170
> [    1.406005]  hpet_time_init+0x2d/0x4b
> [    1.409661]  x86_late_time_init+0x17/0x34
> [    1.413658]  start_kernel+0x8cf/0x97f

The software resend code does not go through the regular interrupt entry
path which explains why get_irq_regs() returns NULL.

That software resend is bogus especially since the timer interrupt is
a level interrupt. As dmesg does not say anything about the APIC
delivery mode I assume this goes through i8259, which fails to set the
IRQ_LEVEL flag on all interrupt lines.

The below should fix this.

Thanks,

        tglx
---
--- a/arch/x86/kernel/i8259.c
+++ b/arch/x86/kernel/i8259.c
@@ -114,6 +114,7 @@ static void make_8259A_irq(unsigned int
 	disable_irq_nosync(irq);
 	io_apic_irqs &= ~(1<<irq);
 	irq_set_chip_and_handler(irq, &i8259A_chip, handle_level_irq);
+	irq_set_status_flags(irq, IRQ_LEVEL);
 	enable_irq(irq);
 	lapic_assign_legacy_vector(irq, true);
 }
--- a/arch/x86/kernel/irqinit.c
+++ b/arch/x86/kernel/irqinit.c
@@ -65,8 +65,10 @@ void __init init_ISA_irqs(void)
 
 	legacy_pic->init(0);
 
-	for (i = 0; i < nr_legacy_irqs(); i++)
+	for (i = 0; i < nr_legacy_irqs(); i++) {
 		irq_set_chip_and_handler(i, chip, handle_level_irq);
+		irq_set_status_flags(i, IRQ_LEVEL);
+	}
 }
 
 void __init init_IRQ(void)