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

tip-bot2 for Peter Zijlstra
2020-05-19T19:53:22Z

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@infradead.org>
AuthorDate: Mon, 24 Feb 2020 22:25:03 +01:00
Committer: Thomas Gleixner <tglx@linutronix.de>
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@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Link: https://lkml.kernel.org/r/20200505134101.139720912@linutronix.de

---
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);
}