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printk: Disallow instrumenting print_nmi_enter()

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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
This commit is contained in:
Peter Zijlstra 2020-02-24 22:25:03 +01:00 committed by Thomas Gleixner
parent 8c4e93c362
commit b0f51883f5
1 changed files with 3 additions and 2 deletions
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5
kernel/printk/printk_safe.c
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@ -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);
}