nmi: create generic NMI backtrace implementation

[linux-2.6-block.git] / lib / nmi_backtrace.c

diff --git a/lib/nmi_backtrace.c b/lib/nmi_backtrace.c
new file mode 100644 (file)
index 0000000..88d3d32
--- /dev/null
+++ b/lib/nmi_backtrace.c
@@ -0,0 +1,162 @@
+/*
+ *  NMI backtrace support
+ *
+ * Gratuitously copied from arch/x86/kernel/apic/hw_nmi.c by Russell King,
+ * with the following header:
+ *
+ *  HW NMI watchdog support
+ *
+ *  started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
+ *
+ *  Arch specific calls to support NMI watchdog
+ *
+ *  Bits copied from original nmi.c file
+ */
+#include <linux/cpumask.h>
+#include <linux/delay.h>
+#include <linux/kprobes.h>
+#include <linux/nmi.h>
+#include <linux/seq_buf.h>
+
+#ifdef arch_trigger_all_cpu_backtrace
+/* For reliability, we're prepared to waste bits here. */
+static DECLARE_BITMAP(backtrace_mask, NR_CPUS) __read_mostly;
+static cpumask_t printtrace_mask;
+
+#define NMI_BUF_SIZE           4096
+
+struct nmi_seq_buf {
+       unsigned char           buffer[NMI_BUF_SIZE];
+       struct seq_buf          seq;
+};
+
+/* Safe printing in NMI context */
+static DEFINE_PER_CPU(struct nmi_seq_buf, nmi_print_seq);
+
+/* "in progress" flag of arch_trigger_all_cpu_backtrace */
+static unsigned long backtrace_flag;
+
+static void print_seq_line(struct nmi_seq_buf *s, int start, int end)
+{
+       const char *buf = s->buffer + start;
+
+       printk("%.*s", (end - start) + 1, buf);
+}
+
+void nmi_trigger_all_cpu_backtrace(bool include_self,
+                                  void (*raise)(cpumask_t *mask))
+{
+       struct nmi_seq_buf *s;
+       int i, cpu, this_cpu = get_cpu();
+
+       if (test_and_set_bit(0, &backtrace_flag)) {
+               /*
+                * If there is already a trigger_all_cpu_backtrace() in progress
+                * (backtrace_flag == 1), don't output double cpu dump infos.
+                */
+               put_cpu();
+               return;
+       }
+
+       cpumask_copy(to_cpumask(backtrace_mask), cpu_online_mask);
+       if (!include_self)
+               cpumask_clear_cpu(this_cpu, to_cpumask(backtrace_mask));
+
+       cpumask_copy(&printtrace_mask, to_cpumask(backtrace_mask));
+
+       /*
+        * Set up per_cpu seq_buf buffers that the NMIs running on the other
+        * CPUs will write to.
+        */
+       for_each_cpu(cpu, to_cpumask(backtrace_mask)) {
+               s = &per_cpu(nmi_print_seq, cpu);
+               seq_buf_init(&s->seq, s->buffer, NMI_BUF_SIZE);
+       }
+
+       if (!cpumask_empty(to_cpumask(backtrace_mask))) {
+               pr_info("Sending NMI to %s CPUs:\n",
+                       (include_self ? "all" : "other"));
+               raise(to_cpumask(backtrace_mask));
+       }
+
+       /* Wait for up to 10 seconds for all CPUs to do the backtrace */
+       for (i = 0; i < 10 * 1000; i++) {
+               if (cpumask_empty(to_cpumask(backtrace_mask)))
+                       break;
+               mdelay(1);
+               touch_softlockup_watchdog();
+       }
+
+       /*
+        * Now that all the NMIs have triggered, we can dump out their
+        * back traces safely to the console.
+        */
+       for_each_cpu(cpu, &printtrace_mask) {
+               int len, last_i = 0;
+
+               s = &per_cpu(nmi_print_seq, cpu);
+               len = seq_buf_used(&s->seq);
+               if (!len)
+                       continue;
+
+               /* Print line by line. */
+               for (i = 0; i < len; i++) {
+                       if (s->buffer[i] == '\n') {
+                               print_seq_line(s, last_i, i);
+                               last_i = i + 1;
+                       }
+               }
+               /* Check if there was a partial line. */
+               if (last_i < len) {
+                       print_seq_line(s, last_i, len - 1);
+                       pr_cont("\n");
+               }
+       }
+
+       clear_bit(0, &backtrace_flag);
+       smp_mb__after_atomic();
+       put_cpu();
+}
+
+/*
+ * It is not safe to call printk() directly from NMI handlers.
+ * It may be fine if the NMI detected a lock up and we have no choice
+ * but to do so, but doing a NMI on all other CPUs to get a back trace
+ * can be done with a sysrq-l. We don't want that to lock up, which
+ * can happen if the NMI interrupts a printk in progress.
+ *
+ * Instead, we redirect the vprintk() to this nmi_vprintk() that writes
+ * the content into a per cpu seq_buf buffer. Then when the NMIs are
+ * all done, we can safely dump the contents of the seq_buf to a printk()
+ * from a non NMI context.
+ */
+static int nmi_vprintk(const char *fmt, va_list args)
+{
+       struct nmi_seq_buf *s = this_cpu_ptr(&nmi_print_seq);
+       unsigned int len = seq_buf_used(&s->seq);
+
+       seq_buf_vprintf(&s->seq, fmt, args);
+       return seq_buf_used(&s->seq) - len;
+}
+
+bool nmi_cpu_backtrace(struct pt_regs *regs)
+{
+       int cpu = smp_processor_id();
+
+       if (cpumask_test_cpu(cpu, to_cpumask(backtrace_mask))) {
+               printk_func_t printk_func_save = this_cpu_read(printk_func);
+
+               /* Replace printk to write into the NMI seq */
+               this_cpu_write(printk_func, nmi_vprintk);
+               pr_warn("NMI backtrace for cpu %d\n", cpu);
+               show_regs(regs);
+               this_cpu_write(printk_func, printk_func_save);
+
+               cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask));
+               return true;
+       }
+
+       return false;
+}
+NOKPROBE_SYMBOL(nmi_cpu_backtrace);
+#endif