[PATCH v26 2/7] arm64: kdump: implement machine_crash_shutdown()
AKASHI Takahiro
takahiro.akashi at linaro.org
Thu Sep 15 20:21:02 PDT 2016
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 at 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 at arm.com>
>
>
> Thanks,
>
> James
>
>
>
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