lib/nmi_backtrace.c

   1 /*
   2  *  NMI backtrace support
   3  *
   4  * Gratuitously copied from arch/x86/kernel/apic/hw_nmi.c by Russell King,
   5  * with the following header:
   6  *
   7  *  HW NMI watchdog support
   8  *
   9  *  started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
  10  *
  11  *  Arch specific calls to support NMI watchdog
  12  *
  13  *  Bits copied from original nmi.c file
  14  */
  15 #include <linux/cpumask.h>
  16 #include <linux/delay.h>
  17 #include <linux/kprobes.h>
  18 #include <linux/nmi.h>
  19 #include <linux/seq_buf.h>
  20
  21 #ifdef arch_trigger_all_cpu_backtrace
  22 /* For reliability, we're prepared to waste bits here. */
  23 static DECLARE_BITMAP(backtrace_mask, NR_CPUS) __read_mostly;
  24 static cpumask_t printtrace_mask;
  25
  26 #define NMI_BUF_SIZE            4096
  27
  28 struct nmi_seq_buf {
  29         unsigned char           buffer[NMI_BUF_SIZE];
  30         struct seq_buf          seq;
  31 };
  32
  33 /* Safe printing in NMI context */
  34 static DEFINE_PER_CPU(struct nmi_seq_buf, nmi_print_seq);
  35
  36 /* "in progress" flag of arch_trigger_all_cpu_backtrace */
  37 static unsigned long backtrace_flag;
  38
  39 static void print_seq_line(struct nmi_seq_buf *s, int start, int end)
  40 {
  41         const char *buf = s->buffer + start;
  42
  43         printk("%.*s", (end - start) + 1, buf);
  44 }
  45
  46 /*
  47  * When raise() is called it will be is passed a pointer to the
  48  * backtrace_mask. Architectures that call nmi_cpu_backtrace()
  49  * directly from their raise() functions may rely on the mask
  50  * they are passed being updated as a side effect of this call.
  51  */
  52 void nmi_trigger_all_cpu_backtrace(bool include_self,
  53                                    void (*raise)(cpumask_t *mask))
  54 {
  55         struct nmi_seq_buf *s;
  56         int i, cpu, this_cpu = get_cpu();
  57
  58         if (test_and_set_bit(0, &backtrace_flag)) {
  59                 /*
  60                  * If there is already a trigger_all_cpu_backtrace() in progress
  61                  * (backtrace_flag == 1), don't output double cpu dump infos.
  62                  */
  63                 put_cpu();
  64                 return;
  65         }
  66
  67         cpumask_copy(to_cpumask(backtrace_mask), cpu_online_mask);
  68         if (!include_self)
  69                 cpumask_clear_cpu(this_cpu, to_cpumask(backtrace_mask));
  70
  71         cpumask_copy(&printtrace_mask, to_cpumask(backtrace_mask));
  72
  73         /*
  74          * Set up per_cpu seq_buf buffers that the NMIs running on the other
  75          * CPUs will write to.
  76          */
  77         for_each_cpu(cpu, to_cpumask(backtrace_mask)) {
  78                 s = &per_cpu(nmi_print_seq, cpu);
  79                 seq_buf_init(&s->seq, s->buffer, NMI_BUF_SIZE);
  80         }
  81
  82         if (!cpumask_empty(to_cpumask(backtrace_mask))) {
  83                 pr_info("Sending NMI to %s CPUs:\n",
  84                         (include_self ? "all" : "other"));
  85                 raise(to_cpumask(backtrace_mask));
  86         }
  87
  88         /* Wait for up to 10 seconds for all CPUs to do the backtrace */
  89         for (i = 0; i < 10 * 1000; i++) {
  90                 if (cpumask_empty(to_cpumask(backtrace_mask)))
  91                         break;
  92                 mdelay(1);
  93                 touch_softlockup_watchdog();
  94         }
  95
  96         /*
  97          * Now that all the NMIs have triggered, we can dump out their
  98          * back traces safely to the console.
  99          */
 100         for_each_cpu(cpu, &printtrace_mask) {
 101                 int len, last_i = 0;
 102
 103                 s = &per_cpu(nmi_print_seq, cpu);
 104                 len = seq_buf_used(&s->seq);
 105                 if (!len)
 106                         continue;
 107
 108                 /* Print line by line. */
 109                 for (i = 0; i < len; i++) {
 110                         if (s->buffer[i] == '\n') {
 111                                 print_seq_line(s, last_i, i);
 112                                 last_i = i + 1;
 113                         }
 114                 }
 115                 /* Check if there was a partial line. */
 116                 if (last_i < len) {
 117                         print_seq_line(s, last_i, len - 1);
 118                         pr_cont("\n");
 119                 }
 120         }
 121
 122         clear_bit(0, &backtrace_flag);
 123         smp_mb__after_atomic();
 124         put_cpu();
 125 }
 126
 127 /*
 128  * It is not safe to call printk() directly from NMI handlers.
 129  * It may be fine if the NMI detected a lock up and we have no choice
 130  * but to do so, but doing a NMI on all other CPUs to get a back trace
 131  * can be done with a sysrq-l. We don't want that to lock up, which
 132  * can happen if the NMI interrupts a printk in progress.
 133  *
 134  * Instead, we redirect the vprintk() to this nmi_vprintk() that writes
 135  * the content into a per cpu seq_buf buffer. Then when the NMIs are
 136  * all done, we can safely dump the contents of the seq_buf to a printk()
 137  * from a non NMI context.
 138  */
 139 static int nmi_vprintk(const char *fmt, va_list args)
 140 {
 141         struct nmi_seq_buf *s = this_cpu_ptr(&nmi_print_seq);
 142         unsigned int len = seq_buf_used(&s->seq);
 143
 144         seq_buf_vprintf(&s->seq, fmt, args);
 145         return seq_buf_used(&s->seq) - len;
 146 }
 147
 148 bool nmi_cpu_backtrace(struct pt_regs *regs)
 149 {
 150         int cpu = smp_processor_id();
 151
 152         if (cpumask_test_cpu(cpu, to_cpumask(backtrace_mask))) {
 153                 printk_func_t printk_func_save = this_cpu_read(printk_func);
 154
 155                 /* Replace printk to write into the NMI seq */
 156                 this_cpu_write(printk_func, nmi_vprintk);
 157                 pr_warn("NMI backtrace for cpu %d\n", cpu);
 158                 if (regs)
 159                         show_regs(regs);
 160                 else
 161                         dump_stack();
 162                 this_cpu_write(printk_func, printk_func_save);
 163
 164                 cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask));
 165                 return true;
 166         }
 167
 168         return false;
 169 }
 170 NOKPROBE_SYMBOL(nmi_cpu_backtrace);
 171 #endif