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// 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;
}
}
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