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// SPDX-License-Identifier: GPL-2.0
/*
* NMI backtrace support
*
* Gratuitously copied from arch/x86/kernel/apic/hw_nmi.c by Russell King,
* with the following header:
*
* HW NMI watchdog support
*
* started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
*
* Arch specific calls to support NMI watchdog
*
* Bits copied from original nmi.c file
*/
#include <linux/cpumask.h>
#include <linux/delay.h>
#include <linux/kprobes.h>
#include <linux/stringify.h>
#include <linux/nmi.h>
#include <linux/cpu.h>
#include <linux/sched/debug.h>
#ifdef arch_trigger_cpumask_backtrace
/* For reliability, we're prepared to waste bits here. */
static DECLARE_BITMAP(backtrace_mask, NR_CPUS) __read_mostly;
/* "in progress" flag of arch_trigger_cpumask_backtrace */
static unsigned long backtrace_flag;
#define NMI_BT_TIMEOUT_SEC 10
/*
* When raise() is called it will be passed a pointer to the
* backtrace_mask. Architectures that call nmi_cpu_backtrace()
* directly from their raise() functions may rely on the mask
* they are passed being updated as a side effect of this call.
*/
void nmi_trigger_cpumask_backtrace(const cpumask_t *mask,
int exclude_cpu,
void (*raise)(cpumask_t *mask))
{
int i, this_cpu = get_cpu();
if (test_and_set_bit(0, &backtrace_flag)) {
/*
* If there is already a trigger_all_cpu_backtrace() in progress
* (backtrace_flag == 1), don't output double cpu dump infos.
*/
put_cpu();
return;
}
cpumask_copy(to_cpumask(backtrace_mask), mask);
if (exclude_cpu != -1)
cpumask_clear_cpu(exclude_cpu, to_cpumask(backtrace_mask));
/*
* Don't try to send an NMI to this cpu; it may work on some
* architectures, but on others it may not, and we'll get
* information at least as useful just by doing a dump_stack() here.
* Note that nmi_cpu_backtrace(NULL) will clear the cpu bit.
*/
if (cpumask_test_cpu(this_cpu, to_cpumask(backtrace_mask)))
nmi_cpu_backtrace(NULL);
if (!cpumask_empty(to_cpumask(backtrace_mask))) {
pr_info("Sending NMI from CPU %d to CPUs %*pbl:\n",
this_cpu, nr_cpumask_bits, to_cpumask(backtrace_mask));
nmi_backtrace_stall_snap(to_cpumask(backtrace_mask));
raise(to_cpumask(backtrace_mask));
}
/* Wait for up to NMI_BT_TIMEOUT_SEC seconds for all CPUs to do the backtrace */
for (i = 0; i < NMI_BT_TIMEOUT_SEC * 1000; i++) {
if (cpumask_empty(to_cpumask(backtrace_mask)))
break;
mdelay(1);
touch_softlockup_watchdog();
}
if (!cpumask_empty(to_cpumask(backtrace_mask))) {
pr_warn("After " __stringify(NMI_BT_TIMEOUT_SEC) " seconds, these CPUS still haven't responded to the NMI: %*pbl\n",
cpumask_pr_args(to_cpumask(backtrace_mask)));
nmi_backtrace_stall_check(to_cpumask(backtrace_mask));
}
/*
* Force flush any remote buffers that might be stuck in IRQ context
* and therefore could not run their irq_work.
*/
printk_trigger_flush();
clear_bit_unlock(0, &backtrace_flag);
put_cpu();
}
// Dump stacks even for idle CPUs.
static bool backtrace_idle;
module_param(backtrace_idle, bool, 0644);
bool nmi_cpu_backtrace(struct pt_regs *regs)
{
int cpu = smp_processor_id();
unsigned long flags;
if (cpumask_test_cpu(cpu, to_cpumask(backtrace_mask))) {
/*
* Allow nested NMI backtraces while serializing
* against other CPUs.
*/
printk_cpu_sync_get_irqsave(flags);
if (!READ_ONCE(backtrace_idle) && regs && cpu_in_idle(instruction_pointer(regs))) {
pr_warn("NMI backtrace for cpu %d skipped: idling at %pS\n",
cpu, (void *)instruction_pointer(regs));
} else {
pr_warn("NMI backtrace for cpu %d\n", cpu);
if (regs)
show_regs(regs);
else
dump_stack();
}
printk_cpu_sync_put_irqrestore(flags);
cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask));
return true;
}
return false;
}
NOKPROBE_SYMBOL(nmi_cpu_backtrace);
#endif
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