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Date:   Mon, 16 Jan 2023 17:08:05 +0800
From:   Baoquan He <bhe@redhat.com>
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     linux-kernel@vger.kernel.org, x86@kernel.org,
        kexec@lists.infradead.org
Subject: Re: kdump kernel randomly hang with tick_periodic call trace on bare
 metal system
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Hi Thomas,

On 01/09/23 at 10:57pm, Thomas Gleixner wrote:
> 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.

I got the machine where this random hang often happen, and built the
latest upstream kernel to test. W/o this fix, kdump kernel will hang 
when calling tick_periodic 6 of 10 times. With this patch applied, I
tried about 30 times, kdump kernel all booted up and vmcore dumping 
succeeded.

So this patch fix the issue I met, thanks a lot. And please feel free to
add:

Tested-by: Baoquan He <bhe@redhat.com>


> 
> ---
> --- 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)
>