1// SPDX-License-Identifier: GPL-2.0-or-later
 2/*
 3 * printk_safe.c - Safe printk for printk-deadlock-prone contexts
 4 */
 5
 6#include <linux/preempt.h>
 7#include <linux/kdb.h>
 8#include <linux/smp.h>
 9#include <linux/cpumask.h>
10#include <linux/printk.h>
11#include <linux/kprobes.h>
12
13#include "internal.h"
14
15static DEFINE_PER_CPU(int, printk_context);
16
17/* Can be preempted by NMI. */
18void __printk_safe_enter(void)
19{
20	this_cpu_inc(printk_context);
21}
22
23/* Can be preempted by NMI. */
24void __printk_safe_exit(void)
25{
26	this_cpu_dec(printk_context);
27}
28
29asmlinkage int vprintk(const char *fmt, va_list args)
30{
31#ifdef CONFIG_KGDB_KDB
32	/* Allow to pass printk() to kdb but avoid a recursion. */
33	if (unlikely(kdb_trap_printk && kdb_printf_cpu < 0))
34		return vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
35#endif
36
37	/*
38	 * Use the main logbuf even in NMI. But avoid calling console
39	 * drivers that might have their own locks.
40	 */
41	if (this_cpu_read(printk_context) || in_nmi()) {
42		int len;
43
44		len = vprintk_store(0, LOGLEVEL_DEFAULT, NULL, fmt, args);
45		defer_console_output();
46		return len;
47	}
48
49	/* No obstacles. */
50	return vprintk_default(fmt, args);
51}
52EXPORT_SYMBOL(vprintk);