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/* Context where printk messages are never suppressed */
16static atomic_t force_con;
17
18void printk_force_console_enter(void)
19{
20 atomic_inc(v: &force_con);
21}
22
23void printk_force_console_exit(void)
24{
25 atomic_dec(v: &force_con);
26}
27
28bool is_printk_force_console(void)
29{
30 return atomic_read(v: &force_con);
31}
32
33static DEFINE_PER_CPU(int, printk_context);
34
35/* Can be preempted by NMI. */
36void __printk_safe_enter(void)
37{
38 this_cpu_inc(printk_context);
39}
40
41/* Can be preempted by NMI. */
42void __printk_safe_exit(void)
43{
44 this_cpu_dec(printk_context);
45}
46
47void __printk_deferred_enter(void)
48{
49 cant_migrate();
50 __printk_safe_enter();
51}
52
53void __printk_deferred_exit(void)
54{
55 cant_migrate();
56 __printk_safe_exit();
57}
58
59bool is_printk_legacy_deferred(void)
60{
61 /*
62 * The per-CPU variable @printk_context can be read safely in any
63 * context. CPU migration is always disabled when set.
64 *
65 * A context holding the printk_cpu_sync must not spin waiting for
66 * another CPU. For legacy printing, it could be the console_lock
67 * or the port lock.
68 */
69 return (force_legacy_kthread() ||
70 this_cpu_read(printk_context) ||
71 in_nmi() ||
72 is_printk_cpu_sync_owner());
73}
74
75asmlinkage int vprintk(const char *fmt, va_list args)
76{
77#ifdef CONFIG_KGDB_KDB
78 /* Allow to pass printk() to kdb but avoid a recursion. */
79 if (unlikely(kdb_trap_printk && kdb_printf_cpu < 0))
80 return vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
81#endif
82 return vprintk_default(fmt, args);
83}
84EXPORT_SYMBOL(vprintk);
85