LXR linux/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. */
  23static DECLARE_BITMAP(backtrace_mask, NR_CPUS) __read_mostly;
  24static cpumask_t printtrace_mask;
  25
  26#define NMI_BUF_SIZE            4096
  27
  28struct nmi_seq_buf {
  29        unsigned char           buffer[NMI_BUF_SIZE];
  30        struct seq_buf          seq;
  31};
  32
  33/* Safe printing in NMI context */
  34static DEFINE_PER_CPU(struct nmi_seq_buf, nmi_print_seq);
  35
  36/* "in progress" flag of arch_trigger_all_cpu_backtrace */
  37static unsigned long backtrace_flag;
  38
  39static 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 */
  52void 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 */
 139static 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
 148bool 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}
 170NOKPROBE_SYMBOL(nmi_cpu_backtrace);
 171#endif
 172