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
15 static DEFINE_PER_CPU(int, printk_context);
16
17 /* Can be preempted by NMI. */
__printk_safe_enter(void)18 void __printk_safe_enter(void)
19 {
20 this_cpu_inc(printk_context);
21 }
22
23 /* Can be preempted by NMI. */
__printk_safe_exit(void)24 void __printk_safe_exit(void)
25 {
26 this_cpu_dec(printk_context);
27 }
28
vprintk(const char * fmt,va_list args)29 asmlinkage 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 }
52 EXPORT_SYMBOL(vprintk);
53
