/*
* 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);
}
/*
* When raise() is called it will be is passed a pointer to the
* backtrace_mask. Architectures that call nmi_cpu_backtrace()
* directly from their raise() functions may rely on the mask
* they are passed being updated as a side effect of this call.
*/
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);
if (regs)
show_regs(regs);
else
dump_stack();
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
