Re: [PATCH v26 2/7] arm64: kdump: implement machine_crash_shutdown()

[AKASHI Takahiro <takahiro.akashi@linaro.org>]

James,

Thank you for your review.

On Wed, Sep 14, 2016 at 07:09:33PM +0100, James Morse wrote:
> Hi Akashi,
> 
> (CC: Marc who knows how this irqchip wizardry works
>  Cover letter: https://www.spinics.net/lists/arm-kernel/msg529520.html )
> 
> On 07/09/16 05:29, AKASHI Takahiro wrote:
> > Primary kernel calls machine_crash_shutdown() to shut down non-boot cpus
> > and save registers' status in per-cpu ELF notes before starting crash
> > dump kernel. See kernel_kexec().
> > Even if not all secondary cpus have shut down, we do kdump anyway.
> > 
> > As we don't have to make non-boot(crashed) cpus offline (to preserve
> > correct status of cpus at crash dump) before shutting down, this patch
> > also adds a variant of smp_send_stop().
> > 
> > Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
> > ---
> >  arch/arm64/include/asm/hardirq.h  |  2 +-
> >  arch/arm64/include/asm/kexec.h    | 41 ++++++++++++++++++++++++-
> >  arch/arm64/include/asm/smp.h      |  2 ++
> >  arch/arm64/kernel/machine_kexec.c | 56 ++++++++++++++++++++++++++++++++--
> >  arch/arm64/kernel/smp.c           | 63 +++++++++++++++++++++++++++++++++++++++
> >  5 files changed, 159 insertions(+), 5 deletions(-)
> > 
> > diff --git a/arch/arm64/include/asm/hardirq.h b/arch/arm64/include/asm/hardirq.h
> > index 8740297..1473fc2 100644
> > --- a/arch/arm64/include/asm/hardirq.h
> > +++ b/arch/arm64/include/asm/hardirq.h
> > @@ -20,7 +20,7 @@
> >  #include <linux/threads.h>
> >  #include <asm/irq.h>
> >  
> > -#define NR_IPI	6
> > +#define NR_IPI	7
> >  
> >  typedef struct {
> >  	unsigned int __softirq_pending;
> > diff --git a/arch/arm64/include/asm/kexec.h b/arch/arm64/include/asm/kexec.h
> > index 04744dc..a908958 100644
> > --- a/arch/arm64/include/asm/kexec.h
> > +++ b/arch/arm64/include/asm/kexec.h
> > @@ -40,7 +40,46 @@
> >  static inline void crash_setup_regs(struct pt_regs *newregs,
> >  				    struct pt_regs *oldregs)
> >  {
> > -	/* Empty routine needed to avoid build errors. */
> > +	if (oldregs) {
> > +		memcpy(newregs, oldregs, sizeof(*newregs));
> > +	} else {
> > +		u64 tmp1, tmp2;
> > +
> > +		__asm__ __volatile__ (
> > +			"stp	 x0,   x1, [%2, #16 *  0]\n"
> > +			"stp	 x2,   x3, [%2, #16 *  1]\n"
> > +			"stp	 x4,   x5, [%2, #16 *  2]\n"
> > +			"stp	 x6,   x7, [%2, #16 *  3]\n"
> > +			"stp	 x8,   x9, [%2, #16 *  4]\n"
> > +			"stp	x10,  x11, [%2, #16 *  5]\n"
> > +			"stp	x12,  x13, [%2, #16 *  6]\n"
> > +			"stp	x14,  x15, [%2, #16 *  7]\n"
> > +			"stp	x16,  x17, [%2, #16 *  8]\n"
> > +			"stp	x18,  x19, [%2, #16 *  9]\n"
> > +			"stp	x20,  x21, [%2, #16 * 10]\n"
> > +			"stp	x22,  x23, [%2, #16 * 11]\n"
> > +			"stp	x24,  x25, [%2, #16 * 12]\n"
> > +			"stp	x26,  x27, [%2, #16 * 13]\n"
> > +			"stp	x28,  x29, [%2, #16 * 14]\n"
> > +			"mov	 %0,  sp\n"
> > +			"stp	x30,  %0,  [%2, #16 * 15]\n"
> > +
> > +			"/* faked current PSTATE */\n"
> > +			"mrs	 %0, CurrentEL\n"
> > +			"mrs	 %1, DAIF\n"
> > +			"orr	 %0, %0, %1\n"
> > +			"mrs	 %1, NZCV\n"
> > +			"orr	 %0, %0, %1\n"
> > +
> 
> What about SPSEL? While we don't use it, it is correctly preserved for
> everything except a CPU that calls panic()...

My comment above might be confusing, but what I want to fake
here is "spsr" as pt_regs.pstate is normally set based on spsr_el1.
So there is no corresponding field of SPSEL in spsr.

> 
> > +			/* pc */
> > +			"adr	 %1, 1f\n"
> > +		"1:\n"
> > +			"stp	 %1, %0,   [%2, #16 * 16]\n"
> > +			: "=r" (tmp1), "=r" (tmp2), "+r" (newregs)
> > +			:
> > +			: "memory"
> > +		);
> > +	}
> >  }
> >  
> >  #endif /* __ASSEMBLY__ */
> > diff --git a/arch/arm64/include/asm/smp.h b/arch/arm64/include/asm/smp.h
> > index 0226447..6b0f2c7 100644
> > --- a/arch/arm64/include/asm/smp.h
> > +++ b/arch/arm64/include/asm/smp.h
> > @@ -136,6 +136,8 @@ static inline void cpu_panic_kernel(void)
> >   */
> >  bool cpus_are_stuck_in_kernel(void);
> >  
> > +extern void smp_send_crash_stop(void);
> > +
> >  #endif /* ifndef __ASSEMBLY__ */
> >  
> >  #endif /* ifndef __ASM_SMP_H */
> > diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c
> > index bc96c8a..8ac9dba8 100644
> > --- a/arch/arm64/kernel/machine_kexec.c
> > +++ b/arch/arm64/kernel/machine_kexec.c
> > @@ -9,6 +9,9 @@
> >   * published by the Free Software Foundation.
> >   */
> >  
> > +#include <linux/interrupt.h>
> > +#include <linux/irq.h>
> > +#include <linux/kernel.h>
> >  #include <linux/kexec.h>
> >  #include <linux/smp.h>
> >  
> > @@ -22,6 +25,7 @@
> >  extern const unsigned char arm64_relocate_new_kernel[];
> >  extern const unsigned long arm64_relocate_new_kernel_size;
> >  
> > +bool in_crash_kexec;
> 
> static?

Yes, it can be.

> >  static unsigned long kimage_start;
> >  
> >  /**
> > @@ -148,7 +152,8 @@ void machine_kexec(struct kimage *kimage)
> >  	/*
> >  	 * New cpus may have become stuck_in_kernel after we loaded the image.
> >  	 */
> > -	BUG_ON(cpus_are_stuck_in_kernel() || (num_online_cpus() > 1));
> > +	BUG_ON((cpus_are_stuck_in_kernel() || (num_online_cpus() > 1)) &&
> > +			!WARN_ON(in_crash_kexec));
> 
> In the kdump case, num_online_cpus() is unchanged as ipi_cpu_crash_stop()
> doesn't update the online cpu masks, so this WARN_ON always fires. This is
> confusing as the 'failed to stop secondary CPUs' message doesn't appear, because
> those CPUs did stop, and waiting_for_crash_ipi has the expected value...

Good catch! I've never noticed that the message was wrong.
The line should be changed to:
	BUG_ON((cpus_are_stuck_in_kernel() || (num_online_cpus() > 1)) &&
			!in_crash_kexec);

> >  
> >  	reboot_code_buffer_phys = page_to_phys(kimage->control_code_page);
> >  	reboot_code_buffer = phys_to_virt(reboot_code_buffer_phys);
> > @@ -200,13 +205,58 @@ void machine_kexec(struct kimage *kimage)
> >  	 * relocation is complete.
> >  	 */
> >  
> > -	cpu_soft_restart(1, reboot_code_buffer_phys, kimage->head,
> > +	cpu_soft_restart(!in_crash_kexec, reboot_code_buffer_phys, kimage->head,
> >  		kimage_start, 0);
> >  
> >  	BUG(); /* Should never get here. */
> >  }
> 
> 
> 
> > +static void machine_kexec_mask_interrupts(void)
> > +{
> > +	unsigned int i;
> > +	struct irq_desc *desc;
> > +
> > +	for_each_irq_desc(i, desc) {
> > +		struct irq_chip *chip;
> > +		int ret;
> > +
> > +		chip = irq_desc_get_chip(desc);
> > +		if (!chip)
> > +			continue;
> > +
> > +		/*
> > +		 * First try to remove the active state. If this
> > +		 * fails, try to EOI the interrupt.
> > +		 */
> > +		ret = irq_set_irqchip_state(i, IRQCHIP_STATE_ACTIVE, false);
> > +
> > +		if (ret && irqd_irq_inprogress(&desc->irq_data) &&
> > +		    chip->irq_eoi)
> > +			chip->irq_eoi(&desc->irq_data);
> > +
> > +		if (chip->irq_mask)
> > +			chip->irq_mask(&desc->irq_data);
> > +
> > +		if (chip->irq_disable && !irqd_irq_disabled(&desc->irq_data))
> > +			chip->irq_disable(&desc->irq_data);
> > +	}
> > +}
> 
> This function is over my head ... I have no idea how this works, I can only
> comment that its different to the version under arch/arm
> 
> /me adds Marc Z to CC.

This function was once borrowed from arch/arm, then dropped temporarily
and revamped based on Marc's comment IIRC.
So I would like to defer to Marc.

> 
> > +/**
> > + * machine_crash_shutdown - shutdown non-crashing cpus and save registers
> > + */
> >  void machine_crash_shutdown(struct pt_regs *regs)
> >  {
> > -	/* Empty routine needed to avoid build errors. */
> > +	local_irq_disable();
> > +
> > +	in_crash_kexec = true;
> > +
> > +	/* shutdown non-crashing cpus */
> > +	smp_send_crash_stop();
> > +
> > +	/* for crashing cpu */
> > +	crash_save_cpu(regs, smp_processor_id());
> > +	machine_kexec_mask_interrupts();
> > +
> > +	pr_info("Starting crashdump kernel...\n");
> >  }
> > diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> > index d93d433..b401b25 100644
> > --- a/arch/arm64/kernel/smp.c
> > +++ b/arch/arm64/kernel/smp.c
> > @@ -37,6 +37,7 @@
> >  #include <linux/completion.h>
> >  #include <linux/of.h>
> >  #include <linux/irq_work.h>
> > +#include <linux/kexec.h>
> >  
> >  #include <asm/alternative.h>
> >  #include <asm/atomic.h>
> > @@ -71,6 +72,7 @@ enum ipi_msg_type {
> >  	IPI_RESCHEDULE,
> >  	IPI_CALL_FUNC,
> >  	IPI_CPU_STOP,
> > +	IPI_CPU_CRASH_STOP,
> >  	IPI_TIMER,
> >  	IPI_IRQ_WORK,
> >  	IPI_WAKEUP
> > @@ -734,6 +736,7 @@ static const char *ipi_types[NR_IPI] __tracepoint_string = {
> >  	S(IPI_RESCHEDULE, "Rescheduling interrupts"),
> >  	S(IPI_CALL_FUNC, "Function call interrupts"),
> >  	S(IPI_CPU_STOP, "CPU stop interrupts"),
> > +	S(IPI_CPU_CRASH_STOP, "CPU stop (for crash dump) interrupts"),
> >  	S(IPI_TIMER, "Timer broadcast interrupts"),
> >  	S(IPI_IRQ_WORK, "IRQ work interrupts"),
> >  	S(IPI_WAKEUP, "CPU wake-up interrupts"),
> > @@ -808,6 +811,29 @@ static void ipi_cpu_stop(unsigned int cpu)
> >  		cpu_relax();
> >  }
> >  
> > +#ifdef CONFIG_KEXEC_CORE
> > +static atomic_t waiting_for_crash_ipi;
> > +#endif
> > +
> > +static void ipi_cpu_crash_stop(unsigned int cpu, struct pt_regs *regs)
> > +{
> > +#ifdef CONFIG_KEXEC_CORE
> > +	crash_save_cpu(regs, cpu);
> > +
> > +	atomic_dec(&waiting_for_crash_ipi);
> > +
> > +	local_irq_disable();
> > +
> > +#ifdef CONFIG_HOTPLUG_CPU
> > +	if (cpu_ops[cpu]->cpu_die)
> > +		cpu_ops[cpu]->cpu_die(cpu);
> > +#endif
> > +
> > +	/* just in case */
> > +	cpu_park_loop();
> > +#endif
> > +}
> > +
> >  /*
> >   * Main handler for inter-processor interrupts
> >   */
> > @@ -838,6 +864,15 @@ void handle_IPI(int ipinr, struct pt_regs *regs)
> >  		irq_exit();
> >  		break;
> >  
> > +	case IPI_CPU_CRASH_STOP:
> > +		if (IS_ENABLED(CONFIG_KEXEC_CORE)) {
> > +			irq_enter();
> > +			ipi_cpu_crash_stop(cpu, regs);
> > +
> > +			unreachable();
> > +		}
> > +		break;
> > +
> >  #ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST
> >  	case IPI_TIMER:
> >  		irq_enter();
> > @@ -910,6 +945,34 @@ void smp_send_stop(void)
> >  			   cpumask_pr_args(cpu_online_mask));
> >  }
> >  
> > +#ifdef CONFIG_KEXEC_CORE
> > +void smp_send_crash_stop(void)
> > +{
> > +	cpumask_t mask;
> > +	unsigned long timeout;
> > +
> > +	if (num_online_cpus() == 1)
> > +		return;
> > +
> > +	cpumask_copy(&mask, cpu_online_mask);
> > +	cpumask_clear_cpu(smp_processor_id(), &mask);
> > +
> > +	atomic_set(&waiting_for_crash_ipi, num_online_cpus() - 1);
> > +
> > +	pr_crit("SMP: stopping secondary CPUs\n");
> > +	smp_cross_call(&mask, IPI_CPU_CRASH_STOP);
> > +
> > +	/* Wait up to one second for other CPUs to stop */
> > +	timeout = USEC_PER_SEC;
> > +	while ((atomic_read(&waiting_for_crash_ipi) > 0) && timeout--)
> > +		udelay(1);
> > +
> > +	if (atomic_read(&waiting_for_crash_ipi) > 0)
> > +		pr_warning("SMP: failed to stop secondary CPUs %*pbl\n",
> > +			   cpumask_pr_args(cpu_online_mask));
> > +}
> > +#endif
> 
> This is very similar to smp_send_stop() which also has the timeout. Is it
> possible to merge them? You could use in_crash_kexec to choose the IPI type.

Yeah, we could merge them along with ipi_cpu_(crash_)stop().
But the resulting code would be quite noisy if each line
is switched by "if (in_crash_kexec)."
Otherwise, we may have one big "if" like:
void smp_send_stop(void)
{
    if (in_crash_kexec)
        ...
    else
        ...
}
It seems to me that it is not much different from the current code.
What do you think?

-Takahiro AKASHI


> 
> > +
> >  /*
> >   * not supported here
> >   */
> > 
> 
> 
> Reviewed-by: James Morse <james.morse@arm.com>
> 
> 
> Thanks,
> 
> James
> 
> 
> 

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