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-rw-r--r--lib/nmi_backtrace.c89
1 files changed, 5 insertions, 84 deletions
diff --git a/lib/nmi_backtrace.c b/lib/nmi_backtrace.c
index 6019c53c669e..26caf51cc238 100644
--- a/lib/nmi_backtrace.c
+++ b/lib/nmi_backtrace.c
@@ -16,33 +16,14 @@
#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()
@@ -52,8 +33,7 @@ static void print_seq_line(struct nmi_seq_buf *s, int start, int end)
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();
+ int i, this_cpu = get_cpu();
if (test_and_set_bit(0, &backtrace_flag)) {
/*
@@ -68,17 +48,6 @@ void nmi_trigger_all_cpu_backtrace(bool include_self,
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"));
@@ -94,73 +63,25 @@ void nmi_trigger_all_cpu_backtrace(bool include_self,
}
/*
- * Now that all the NMIs have triggered, we can dump out their
- * back traces safely to the console.
+ * Force flush any remote buffers that might be stuck in IRQ context
+ * and therefore could not run their irq_work.
*/
- for_each_cpu(cpu, &printtrace_mask) {
- int len, last_i = 0;
+ printk_nmi_flush();
- 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();
+ clear_bit_unlock(0, &backtrace_flag);
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;
}