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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/kprobes.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);
}
void __printk_deferred_enter(void)
{
cant_migrate();
__printk_safe_enter();
}
void __printk_deferred_exit(void)
{
cant_migrate();
__printk_safe_exit();
}
bool is_printk_legacy_deferred(void)
{
/*
* The per-CPU variable @printk_context can be read safely in any
* context. CPU migration is always disabled when set.
*/
return (this_cpu_read(printk_context) || in_nmi());
}
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 (is_printk_legacy_deferred())
return vprintk_deferred(fmt, args);
/* No obstacles. */
return vprintk_default(fmt, args);
}
EXPORT_SYMBOL(vprintk);
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