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85e3e7fbbb
All NMI contexts are handled the same as the safe context: store the
message and defer printing. There is no need to have special NMI
context tracking for this. Using in_nmi() is enough.
There are several parts of the kernel that are manually calling into
the printk NMI context tracking in order to cause general printk
deferred printing:
arch/arm/kernel/smp.c
arch/powerpc/kexec/crash.c
kernel/trace/trace.c
For arm/kernel/smp.c and powerpc/kexec/crash.c, provide a new
function pair printk_deferred_enter/exit that explicitly achieves the
same objective.
For ftrace, remove the printk context manipulation completely. It was
added in commit 03fc7f9c99c1 ("printk/nmi: Prevent deadlock when
accessing the main log buffer in NMI"). The purpose was to enforce
storing messages directly into the ring buffer even in NMI context.
It really should have only modified the behavior in NMI context.
There is no need for a special behavior any longer. All messages are
always stored directly now. The console deferring is handled
transparently in vprintk().
Signed-off-by: John Ogness <john.ogness@linutronix.de>
[pmladek@suse.com: Remove special handling in ftrace.c completely.
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20210715193359.25946-5-john.ogness@linutronix.de
53 lines
1.1 KiB
C
53 lines
1.1 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* printk_safe.c - Safe printk for printk-deadlock-prone contexts
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*/
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#include <linux/preempt.h>
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#include <linux/kdb.h>
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#include <linux/smp.h>
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#include <linux/cpumask.h>
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#include <linux/printk.h>
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#include <linux/kprobes.h>
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#include "internal.h"
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static DEFINE_PER_CPU(int, printk_context);
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/* Can be preempted by NMI. */
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void __printk_safe_enter(void)
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{
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this_cpu_inc(printk_context);
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}
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/* Can be preempted by NMI. */
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void __printk_safe_exit(void)
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{
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this_cpu_dec(printk_context);
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}
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asmlinkage int vprintk(const char *fmt, va_list args)
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{
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#ifdef CONFIG_KGDB_KDB
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/* Allow to pass printk() to kdb but avoid a recursion. */
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if (unlikely(kdb_trap_printk && kdb_printf_cpu < 0))
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return vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
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#endif
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/*
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* Use the main logbuf even in NMI. But avoid calling console
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* drivers that might have their own locks.
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*/
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if (this_cpu_read(printk_context) || in_nmi()) {
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int len;
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len = vprintk_store(0, LOGLEVEL_DEFAULT, NULL, fmt, args);
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defer_console_output();
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return len;
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}
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/* No obstacles. */
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return vprintk_default(fmt, args);
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}
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EXPORT_SYMBOL(vprintk);
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