[tip: core/rcu] printk: Disallow instrumenting print_nmi_enter()

[tip-bot2 for Peter Zijlstra]

The following commit has been merged into the core/rcu branch of tip:

Commit-ID:     b0f51883f551b900a04a80f49fb0886caf7e9a12
Gitweb:        https://git.kernel.org/tip/b0f51883f551b900a04a80f49fb0886caf7e9a12
Author:        Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate:    Mon, 24 Feb 2020 22:25:03 +01:00
Committer:     Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Tue, 19 May 2020 15:51:16 +02:00

printk: Disallow instrumenting print_nmi_enter()

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@xxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reviewed-by: Alexandre Chartre <alexandre.chartre@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20200505134101.139720912@xxxxxxxxxxxxx


---
 kernel/printk/printk_safe.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c
index e8791f2..4242403 100644
--- 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(const char *fmt, va_list args)
 	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);
 }