lib/nmi_backtrace.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  *  NMI backtrace support
   4  *
   5  * Gratuitously copied from arch/x86/kernel/apic/hw_nmi.c by Russell King,
   6  * with the following header:
   7  *
   8  *  HW NMI watchdog support
   9  *
  10  *  started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
  11  *
  12  *  Arch specific calls to support NMI watchdog
  13  *
  14  *  Bits copied from original nmi.c file
  15  */
  16 #include <linux/cpumask.h>
  17 #include <linux/delay.h>
  18 #include <linux/kprobes.h>
  19 #include <linux/nmi.h>
  20 #include <linux/cpu.h>
  21 #include <linux/sched/debug.h>
  22
  23 #ifdef arch_trigger_cpumask_backtrace
  24 /* For reliability, we're prepared to waste bits here. */
  25 static DECLARE_BITMAP(backtrace_mask, NR_CPUS) __read_mostly;
  26
  27 /* "in progress" flag of arch_trigger_cpumask_backtrace */
  28 static unsigned long backtrace_flag;
  29
  30 /*
  31  * When raise() is called it will be passed a pointer to the
  32  * backtrace_mask. Architectures that call nmi_cpu_backtrace()
  33  * directly from their raise() functions may rely on the mask
  34  * they are passed being updated as a side effect of this call.
  35  */
  36 void nmi_trigger_cpumask_backtrace(const cpumask_t *mask,
  37                                    bool exclude_self,
  38                                    void (*raise)(cpumask_t *mask))
  39 {
  40         int i, this_cpu = get_cpu();
  41
  42         if (test_and_set_bit(0, &backtrace_flag)) {
  43                 /*
  44                  * If there is already a trigger_all_cpu_backtrace() in progress
  45                  * (backtrace_flag == 1), don't output double cpu dump infos.
  46                  */
  47                 put_cpu();
  48                 return;
  49         }
  50
  51         cpumask_copy(to_cpumask(backtrace_mask), mask);
  52         if (exclude_self)
  53                 cpumask_clear_cpu(this_cpu, to_cpumask(backtrace_mask));
  54
  55         /*
  56          * Don't try to send an NMI to this cpu; it may work on some
  57          * architectures, but on others it may not, and we'll get
  58          * information at least as useful just by doing a dump_stack() here.
  59          * Note that nmi_cpu_backtrace(NULL) will clear the cpu bit.
  60          */
  61         if (cpumask_test_cpu(this_cpu, to_cpumask(backtrace_mask)))
  62                 nmi_cpu_backtrace(NULL);
  63
  64         if (!cpumask_empty(to_cpumask(backtrace_mask))) {
  65                 pr_info("Sending NMI from CPU %d to CPUs %*pbl:\n",
  66                         this_cpu, nr_cpumask_bits, to_cpumask(backtrace_mask));
  67                 raise(to_cpumask(backtrace_mask));
  68         }
  69
  70         /* Wait for up to 10 seconds for all CPUs to do the backtrace */
  71         for (i = 0; i < 10 * 1000; i++) {
  72                 if (cpumask_empty(to_cpumask(backtrace_mask)))
  73                         break;
  74                 mdelay(1);
  75                 touch_softlockup_watchdog();
  76         }
  77
  78         /*
  79          * Force flush any remote buffers that might be stuck in IRQ context
  80          * and therefore could not run their irq_work.
  81          */
  82         printk_trigger_flush();
  83
  84         clear_bit_unlock(0, &backtrace_flag);
  85         put_cpu();
  86 }
  87
  88 // Dump stacks even for idle CPUs.
  89 static bool backtrace_idle;
  90 module_param(backtrace_idle, bool, 0644);
  91
  92 bool nmi_cpu_backtrace(struct pt_regs *regs)
  93 {
  94         int cpu = smp_processor_id();
  95         unsigned long flags;
  96
  97         if (cpumask_test_cpu(cpu, to_cpumask(backtrace_mask))) {
  98                 /*
  99                  * Allow nested NMI backtraces while serializing
 100                  * against other CPUs.
 101                  */
 102                 printk_cpu_sync_get_irqsave(flags);
 103                 if (!READ_ONCE(backtrace_idle) && regs && cpu_in_idle(instruction_pointer(regs))) {
 104                         pr_warn("NMI backtrace for cpu %d skipped: idling at %pS\n",
 105                                 cpu, (void *)instruction_pointer(regs));
 106                 } else {
 107                         pr_warn("NMI backtrace for cpu %d\n", cpu);
 108                         if (regs)
 109                                 show_regs(regs);
 110                         else
 111                                 dump_stack();
 112                 }
 113                 printk_cpu_sync_put_irqrestore(flags);
 114                 cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask));
 115                 return true;
 116         }
 117
 118         return false;
 119 }
 120 NOKPROBE_SYMBOL(nmi_cpu_backtrace);
 121 #endif