| 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. */ |
| 18 | void __printk_safe_enter(void) |
| 19 | { |
| 20 | this_cpu_inc(printk_context); |
| 21 | } |
| 22 | |
| 23 | /* Can be preempted by NMI. */ |
| 24 | void __printk_safe_exit(void) |
| 25 | { |
| 26 | this_cpu_dec(printk_context); |
| 27 | } |
| 28 | |
| 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(src: 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 | return vprintk_deferred(fmt, args); |
| 43 | |
| 44 | /* No obstacles. */ |
| 45 | return vprintk_default(fmt, args); |
| 46 | } |
| 47 | EXPORT_SYMBOL(vprintk); |
| 48 |