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                                    int exclude_cpu,
  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_cpu != -1)
  53                 cpumask_clear_cpu(exclude_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                 nmi_backtrace_stall_snap(to_cpumask(backtrace_mask));
  68                 raise(to_cpumask(backtrace_mask));
  69         }
  70
  71         /* Wait for up to 10 seconds for all CPUs to do the backtrace */
  72         for (i = 0; i < 10 * 1000; i++) {
  73                 if (cpumask_empty(to_cpumask(backtrace_mask)))
  74                         break;
  75                 mdelay(1);
  76                 touch_softlockup_watchdog();
  77         }
  78         nmi_backtrace_stall_check(to_cpumask(backtrace_mask));
  79
  80         /*
  81          * Force flush any remote buffers that might be stuck in IRQ context
  82          * and therefore could not run their irq_work.
  83          */
  84         printk_trigger_flush();
  85
  86         clear_bit_unlock(0, &backtrace_flag);
  87         put_cpu();
  88 }
  89
  90 // Dump stacks even for idle CPUs.
  91 static bool backtrace_idle;
  92 module_param(backtrace_idle, bool, 0644);
  93
  94 bool nmi_cpu_backtrace(struct pt_regs *regs)
  95 {
  96         int cpu = smp_processor_id();
  97         unsigned long flags;
  98
  99         if (cpumask_test_cpu(cpu, to_cpumask(backtrace_mask))) {
 100                 /*
 101                  * Allow nested NMI backtraces while serializing
 102                  * against other CPUs.
 103                  */
 104                 printk_cpu_sync_get_irqsave(flags);
 105                 if (!READ_ONCE(backtrace_idle) && regs && cpu_in_idle(instruction_pointer(regs))) {
 106                         pr_warn("NMI backtrace for cpu %d skipped: idling at %pS\n",
 107                                 cpu, (void *)instruction_pointer(regs));
 108                 } else {
 109                         pr_warn("NMI backtrace for cpu %d\n", cpu);
 110                         if (regs)
 111                                 show_regs(regs);
 112                         else
 113                                 dump_stack();
 114                 }
 115                 printk_cpu_sync_put_irqrestore(flags);
 116                 cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask));
 117                 return true;
 118         }
 119
 120         return false;
 121 }
 122 NOKPROBE_SYMBOL(nmi_cpu_backtrace);
 123 #endif