[patch V4 part 1 31/36] printk: Disallow instrumenting print_nmi_enter()

Thomas Gleixner
2020-05-05T14:22:58Z

From: Peter Zijlstra <peterz@infradead.org>

It happens early in nmi_enter(), no tracing, probing or other funnies
allowed. Specifically as nmi_enter() will be used in do_debug(), which
would cause recursive exceptions when kprobed.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
kernel/printk/printk_safe.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

--- a/kernel/printk/printk_safe.c
+++ b/kernel/printk/printk_safe.c
@@ -10,6 +10,7 @@
#include <linux/cpumask.h>
#include <linux/irq_work.h>
#include <linux/printk.h>
+#include <linux/kprobes.h>

#include "internal.h"

@@ -293,12 +294,12 @@ static __printf(1, 0) int vprintk_nmi(co
return printk_safe_log_store(s, fmt, args);
}

-void notrace printk_nmi_enter(void)
+void noinstr printk_nmi_enter(void)
{
this_cpu_add(printk_context, PRINTK_NMI_CONTEXT_OFFSET);
}

-void notrace printk_nmi_exit(void)
+void noinstr printk_nmi_exit(void)
{
this_cpu_sub(printk_context, PRINTK_NMI_CONTEXT_OFFSET);
}