[PATCH 11/15] arm64: kdump: implement machine_crash_shutdown()
AKASHI Takahiro
takahiro.akashi at linaro.org
Mon Nov 9 17:23:56 PST 2015
On 11/07/2015 04:14 AM, Geoff Levand wrote:
> From: AKASHI Takahiro <takahiro.akashi at linaro.org>
>
> kdump calls machine_crash_shutdown() to shut down non-boot cpus and
> save registers' status in per-cpu ELF notes before starting the crash
> dump kernel. See kernel_kexec().
>
> ipi_cpu_stop() is a bit modified and used to support this behavior.
I've got some concerns of using ipi_cpu_stop().
> Signed-off-by: AKASHI Takahiro <takahiro.akashi at linaro.org>
> ---
> arch/arm64/include/asm/kexec.h | 34 +++++++++++++++++++++++++++++++++-
> arch/arm64/kernel/machine_kexec.c | 31 +++++++++++++++++++++++++++++--
> arch/arm64/kernel/smp.c | 16 ++++++++++++++--
> 3 files changed, 76 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kexec.h b/arch/arm64/include/asm/kexec.h
> index 46d63cd..555a955 100644
> --- a/arch/arm64/include/asm/kexec.h
> +++ b/arch/arm64/include/asm/kexec.h
> @@ -30,6 +30,8 @@
>
> #if !defined(__ASSEMBLY__)
>
> +extern bool in_crash_kexec;
> +
> /**
> * crash_setup_regs() - save registers for the panic kernel
> *
> @@ -40,7 +42,37 @@
> 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 {
> + __asm__ __volatile__ (
> + "stp x0, x1, [%3, #16 * 0]\n"
> + "stp x2, x3, [%3, #16 * 1]\n"
> + "stp x4, x5, [%3, #16 * 2]\n"
> + "stp x6, x7, [%3, #16 * 3]\n"
> + "stp x8, x9, [%3, #16 * 4]\n"
> + "stp x10, x11, [%3, #16 * 5]\n"
> + "stp x12, x13, [%3, #16 * 6]\n"
> + "stp x14, x15, [%3, #16 * 7]\n"
> + "stp x16, x17, [%3, #16 * 8]\n"
> + "stp x18, x19, [%3, #16 * 9]\n"
> + "stp x20, x21, [%3, #16 * 10]\n"
> + "stp x22, x23, [%3, #16 * 11]\n"
> + "stp x24, x25, [%3, #16 * 12]\n"
> + "stp x26, x27, [%3, #16 * 13]\n"
> + "stp x28, x29, [%3, #16 * 14]\n"
> + "str x30, [%3, #16 * 15]\n"
> + "mov %0, sp\n"
> + "adr %1, 1f\n"
> + "mrs %2, spsr_el1\n"
> + "1:"
> + : "=r" (newregs->sp),
> + "=r" (newregs->pc),
> + "=r" (newregs->pstate)
> + : "r" (&newregs->regs)
> + : "memory"
> + );
> + }
> }
>
> #endif /* !defined(__ASSEMBLY__) */
> diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c
> index da28a26..d2d7e90 100644
> --- a/arch/arm64/kernel/machine_kexec.c
> +++ b/arch/arm64/kernel/machine_kexec.c
> @@ -9,6 +9,7 @@
> * published by the Free Software Foundation.
> */
>
> +#include <linux/kernel.h>
> #include <linux/kexec.h>
> #include <linux/of_fdt.h>
> #include <linux/slab.h>
> @@ -23,6 +24,7 @@
> extern const unsigned char arm64_relocate_new_kernel[];
> extern const unsigned long arm64_relocate_new_kernel_size;
>
> +bool in_crash_kexec;
> static unsigned long kimage_start;
>
> /**
> @@ -203,13 +205,38 @@ void machine_kexec(struct kimage *kimage)
> */
>
> cpu_soft_restart(virt_to_phys(cpu_reset),
> - is_hyp_mode_available(),
> + in_crash_kexec ? 0 : is_hyp_mode_available(),
> reboot_code_buffer_phys, kimage->head, kimage_start);
>
> BUG(); /* Should never get here. */
> }
>
> +/**
> + * machine_crash_shutdown - shutdown non-boot cpus and save registers
> + */
> void machine_crash_shutdown(struct pt_regs *regs)
> {
> - /* Empty routine needed to avoid build errors. */
> + struct pt_regs dummy_regs;
> + int cpu;
> +
> + local_irq_disable();
> +
> + in_crash_kexec = true;
> +
> + /*
> + * clear and initialize the per-cpu info. This is necessary
> + * because, otherwise, slots for offline cpus would never be
> + * filled up. See smp_send_stop().
> + */
> + memset(&dummy_regs, 0, sizeof(dummy_regs));
> + for_each_possible_cpu(cpu)
> + crash_save_cpu(&dummy_regs, cpu);
> +
> + /* shutdown non-boot cpus */
> + smp_send_stop();
> +
> + /* for boot cpu */
> + crash_save_cpu(regs, smp_processor_id());
> +
> + pr_info("Starting crashdump kernel...\n");
> }
> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> index dbdaacd..88aec66 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>
> @@ -54,6 +55,8 @@
> #include <asm/ptrace.h>
> #include <asm/virt.h>
>
> +#include "cpu-reset.h"
> +
> #define CREATE_TRACE_POINTS
> #include <trace/events/ipi.h>
>
> @@ -679,8 +682,12 @@ static DEFINE_RAW_SPINLOCK(stop_lock);
> /*
> * ipi_cpu_stop - handle IPI from smp_send_stop()
> */
> -static void ipi_cpu_stop(unsigned int cpu)
> +static void ipi_cpu_stop(unsigned int cpu, struct pt_regs *regs)
> {
> +#ifdef CONFIG_KEXEC
> + /* printing messages may slow down the shutdown. */
> + if (!in_crash_kexec)
> +#endif
> if (system_state == SYSTEM_BOOTING ||
> system_state == SYSTEM_RUNNING) {
> raw_spin_lock(&stop_lock);
> @@ -693,6 +700,11 @@ static void ipi_cpu_stop(unsigned int cpu)
>
> local_irq_disable();
>
> +#ifdef CONFIG_KEXEC
> + if (in_crash_kexec)
> + crash_save_cpu(regs, cpu);
> +#endif /* CONFIG_KEXEC */
> +
> while (1)
> cpu_relax();
> }
cpu_relax() is defined as asm("yield"), and this puts all but boot cpu into
a infinite loop of nop (actually, whether nop or other depends on hw implementation).
Thus all the secondary cpus are still running busy loop even after crash dump kernel
has started up, and the chip can potentially get overheated.
I ran into this situation when I tested the code on Hikey, and the system was
forced to be shut down by thermal driver.
So I'd like to modify the code a bit like:
if (in_crash_kernel {
crash_save_cpu(regs, cpu);
while (1)
asm("wfi"); /* irq is disabled here. */
}
Does this make sense?
-Takahiro AKASHI
> @@ -723,7 +735,7 @@ void handle_IPI(int ipinr, struct pt_regs *regs)
>
> case IPI_CPU_STOP:
> irq_enter();
> - ipi_cpu_stop(cpu);
> + ipi_cpu_stop(cpu, regs);
> irq_exit();
> break;
>
>
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