arch/x86/kernel/apic/hw_nmi.c

   1 /*
   2  *  HW NMI watchdog support
   3  *
   4  *  started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
   5  *
   6  *  Arch specific calls to support NMI watchdog
   7  *
   8  *  Bits copied from original nmi.c file
   9  *
  10  */
  11 #include <asm/apic.h>
  12 #include <asm/nmi.h>
  13
  14 #include <linux/cpumask.h>
  15 #include <linux/kdebug.h>
  16 #include <linux/notifier.h>
  17 #include <linux/kprobes.h>
  18 #include <linux/nmi.h>
  19 #include <linux/module.h>
  20 #include <linux/delay.h>
  21 #include <linux/seq_buf.h>
  22
  23 #ifdef CONFIG_HARDLOCKUP_DETECTOR
  24 u64 hw_nmi_get_sample_period(int watchdog_thresh)
  25 {
  26         return (u64)(cpu_khz) * 1000 * watchdog_thresh;
  27 }
  28 #endif
  29
  30 #ifdef arch_trigger_all_cpu_backtrace
  31 /* For reliability, we're prepared to waste bits here. */
  32 static DECLARE_BITMAP(backtrace_mask, NR_CPUS) __read_mostly;
  33 static cpumask_t printtrace_mask;
  34
  35 #define NMI_BUF_SIZE            4096
  36
  37 struct nmi_seq_buf {
  38         unsigned char           buffer[NMI_BUF_SIZE];
  39         struct seq_buf          seq;
  40 };
  41
  42 /* Safe printing in NMI context */
  43 static DEFINE_PER_CPU(struct nmi_seq_buf, nmi_print_seq);
  44
  45 /* "in progress" flag of arch_trigger_all_cpu_backtrace */
  46 static unsigned long backtrace_flag;
  47
  48 static void print_seq_line(struct nmi_seq_buf *s, int start, int end)
  49 {
  50         const char *buf = s->buffer + start;
  51
  52         printk("%.*s", (end - start) + 1, buf);
  53 }
  54
  55 void arch_trigger_all_cpu_backtrace(bool include_self)
  56 {
  57         struct nmi_seq_buf *s;
  58         int len;
  59         int cpu;
  60         int i;
  61         int this_cpu = get_cpu();
  62
  63         if (test_and_set_bit(0, &backtrace_flag)) {
  64                 /*
  65                  * If there is already a trigger_all_cpu_backtrace() in progress
  66                  * (backtrace_flag == 1), don't output double cpu dump infos.
  67                  */
  68                 put_cpu();
  69                 return;
  70         }
  71
  72         cpumask_copy(to_cpumask(backtrace_mask), cpu_online_mask);
  73         if (!include_self)
  74                 cpumask_clear_cpu(this_cpu, to_cpumask(backtrace_mask));
  75
  76         cpumask_copy(&printtrace_mask, to_cpumask(backtrace_mask));
  77         /*
  78          * Set up per_cpu seq_buf buffers that the NMIs running on the other
  79          * CPUs will write to.
  80          */
  81         for_each_cpu(cpu, to_cpumask(backtrace_mask)) {
  82                 s = &per_cpu(nmi_print_seq, cpu);
  83                 seq_buf_init(&s->seq, s->buffer, NMI_BUF_SIZE);
  84         }
  85
  86         if (!cpumask_empty(to_cpumask(backtrace_mask))) {
  87                 pr_info("sending NMI to %s CPUs:\n",
  88                         (include_self ? "all" : "other"));
  89                 apic->send_IPI_mask(to_cpumask(backtrace_mask), NMI_VECTOR);
  90         }
  91
  92         /* Wait for up to 10 seconds for all CPUs to do the backtrace */
  93         for (i = 0; i < 10 * 1000; i++) {
  94                 if (cpumask_empty(to_cpumask(backtrace_mask)))
  95                         break;
  96                 mdelay(1);
  97                 touch_softlockup_watchdog();
  98         }
  99
 100         /*
 101          * Now that all the NMIs have triggered, we can dump out their
 102          * back traces safely to the console.
 103          */
 104         for_each_cpu(cpu, &printtrace_mask) {
 105                 int last_i = 0;
 106
 107                 s = &per_cpu(nmi_print_seq, cpu);
 108                 len = seq_buf_used(&s->seq);
 109                 if (!len)
 110                         continue;
 111
 112                 /* Print line by line. */
 113                 for (i = 0; i < len; i++) {
 114                         if (s->buffer[i] == '\n') {
 115                                 print_seq_line(s, last_i, i);
 116                                 last_i = i + 1;
 117                         }
 118                 }
 119                 /* Check if there was a partial line. */
 120                 if (last_i < len) {
 121                         print_seq_line(s, last_i, len - 1);
 122                         pr_cont("\n");
 123                 }
 124         }
 125
 126         clear_bit(0, &backtrace_flag);
 127         smp_mb__after_atomic();
 128         put_cpu();
 129 }
 130
 131 /*
 132  * It is not safe to call printk() directly from NMI handlers.
 133  * It may be fine if the NMI detected a lock up and we have no choice
 134  * but to do so, but doing a NMI on all other CPUs to get a back trace
 135  * can be done with a sysrq-l. We don't want that to lock up, which
 136  * can happen if the NMI interrupts a printk in progress.
 137  *
 138  * Instead, we redirect the vprintk() to this nmi_vprintk() that writes
 139  * the content into a per cpu seq_buf buffer. Then when the NMIs are
 140  * all done, we can safely dump the contents of the seq_buf to a printk()
 141  * from a non NMI context.
 142  */
 143 static int nmi_vprintk(const char *fmt, va_list args)
 144 {
 145         struct nmi_seq_buf *s = this_cpu_ptr(&nmi_print_seq);
 146         unsigned int len = seq_buf_used(&s->seq);
 147
 148         seq_buf_vprintf(&s->seq, fmt, args);
 149         return seq_buf_used(&s->seq) - len;
 150 }
 151
 152 static int
 153 arch_trigger_all_cpu_backtrace_handler(unsigned int cmd, struct pt_regs *regs)
 154 {
 155         int cpu;
 156
 157         cpu = smp_processor_id();
 158
 159         if (cpumask_test_cpu(cpu, to_cpumask(backtrace_mask))) {
 160                 printk_func_t printk_func_save = this_cpu_read(printk_func);
 161
 162                 /* Replace printk to write into the NMI seq */
 163                 this_cpu_write(printk_func, nmi_vprintk);
 164                 printk(KERN_WARNING "NMI backtrace for cpu %d\n", cpu);
 165                 show_regs(regs);
 166                 this_cpu_write(printk_func, printk_func_save);
 167
 168                 cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask));
 169                 return NMI_HANDLED;
 170         }
 171
 172         return NMI_DONE;
 173 }
 174 NOKPROBE_SYMBOL(arch_trigger_all_cpu_backtrace_handler);
 175
 176 static int __init register_trigger_all_cpu_backtrace(void)
 177 {
 178         register_nmi_handler(NMI_LOCAL, arch_trigger_all_cpu_backtrace_handler,
 179                                 0, "arch_bt");
 180         return 0;
 181 }
 182 early_initcall(register_trigger_all_cpu_backtrace);
 183 #endif