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

[James Morse <james.morse@arm.com>]

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()...


> +			/* 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?


>  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...


>  
>  	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.


> +/**
> + * 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.


> +
>  /*
>   * not supported here
>   */
> 


Reviewed-by: James Morse <james.morse@arm.com>


Thanks,

James




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