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(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