| // SPDX-License-Identifier: GPL-2.0-or-later |
| /* |
| * printk_safe.c - Safe printk for printk-deadlock-prone contexts |
| */ |
| |
| #include <linux/preempt.h> |
| #include <linux/kdb.h> |
| #include <linux/smp.h> |
| #include <linux/cpumask.h> |
| #include <linux/printk.h> |
| #include <linux/console.h> |
| #include <linux/kprobes.h> |
| #include <linux/delay.h> |
| |
| #include "internal.h" |
| |
| static DEFINE_PER_CPU(int, printk_context); |
| |
| /* Can be preempted by NMI. */ |
| void __printk_safe_enter(void) |
| { |
| this_cpu_inc(printk_context); |
| } |
| |
| /* Can be preempted by NMI. */ |
| void __printk_safe_exit(void) |
| { |
| this_cpu_dec(printk_context); |
| } |
| |
| asmlinkage int vprintk(const char *fmt, va_list args) |
| { |
| #ifdef CONFIG_KGDB_KDB |
| /* Allow to pass printk() to kdb but avoid a recursion. */ |
| if (unlikely(kdb_trap_printk && kdb_printf_cpu < 0)) |
| return vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args); |
| #endif |
| |
| /* |
| * Use the main logbuf even in NMI. But avoid calling console |
| * drivers that might have their own locks. |
| */ |
| if (this_cpu_read(printk_context) || in_nmi()) { |
| int len; |
| |
| len = vprintk_store(0, LOGLEVEL_DEFAULT, NULL, fmt, args); |
| defer_console_output(); |
| return len; |
| } |
| |
| /* No obstacles. */ |
| return vprintk_default(fmt, args); |
| } |
| EXPORT_SYMBOL(vprintk); |
| |
| /** |
| * try_block_console_kthreads() - Try to block console kthreads and |
| * make the global console_lock() avaialble |
| * |
| * @timeout_ms: The maximum time (in ms) to wait. |
| * |
| * Prevent console kthreads from starting processing new messages. Wait |
| * until the global console_lock() become available. |
| * |
| * Context: Can be called in any context. |
| */ |
| void try_block_console_kthreads(int timeout_ms) |
| { |
| block_console_kthreads = true; |
| |
| /* Do not wait when the console lock could not be safely taken. */ |
| if (this_cpu_read(printk_context) || in_nmi()) |
| return; |
| |
| while (timeout_ms > 0) { |
| if (console_trylock()) { |
| console_unlock(); |
| return; |
| } |
| |
| udelay(1000); |
| timeout_ms -= 1; |
| } |
| } |