printk/kdb: Redirect printk messages into kdb in any context (2a9e5ded) · Commits · 戴 / test

kdb has to get messages on consoles even when the system is stopped. It uses kdb_printf() internally and calls console drivers on its own. It uses a hack to reuse an existing code. It sets "kdb_trap_printk" global variable to redirect even the normal printk() into the kdb_printf() variant. The variable "kdb_trap_printk" is checked in printk_default() and it is ignored when printk is redirected to printk_safe in NMI context. Solve this by moving the check into printk_func(). It is obvious that it is not fully safe. But it does not make things worse. The console drivers are already called in this context by db_printf() direct calls. Reported-by:

Sumit Garg <sumit.garg@linaro.org> Tested-by:

Sumit Garg <sumit.garg@linaro.org> Reviewed-by:

Daniel Thompson <daniel.thompson@linaro.org> Acked-by:

Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Signed-off-by:

Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20200520102233.GC3464@linux-b0ei

kernel/printk/printk.c

+1 −13

Original line number	Diff line number	Diff line
		@@ -35,7 +35,6 @@
		#include <linux/memblock.h>
		#include <linux/syscalls.h>
		#include <linux/crash_core.h>
		#include <linux/kdb.h>
		#include <linux/ratelimit.h>
		#include <linux/kmsg_dump.h>
		#include <linux/syslog.h>
		@@ -2047,18 +2046,7 @@ EXPORT_SYMBOL(vprintk);

		int vprintk_default(const char *fmt, va_list args)
		{
		int r;

		#ifdef CONFIG_KGDB_KDB
		/* Allow to pass printk() to kdb but avoid a recursion. */
		if (unlikely(kdb_trap_printk && kdb_printf_cpu < 0)) {
		r = vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
		return r;
		}
		#endif
		r = vprintk_emit(0, LOGLEVEL_DEFAULT, NULL, 0, fmt, args);

		return r;
		return vprintk_emit(0, LOGLEVEL_DEFAULT, NULL, 0, fmt, args);
		}
		EXPORT_SYMBOL_GPL(vprintk_default);

kernel/printk/printk_safe.c

+7 −0

Original line number	Diff line number	Diff line
		@@ -6,6 +6,7 @@
		#include <linux/preempt.h>
		#include <linux/spinlock.h>
		#include <linux/debug_locks.h>
		#include <linux/kdb.h>
		#include <linux/smp.h>
		#include <linux/cpumask.h>
		#include <linux/irq_work.h>
		@@ -359,6 +360,12 @@ void __printk_safe_exit(void)

		__printf(1, 0) int vprintk_func(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

		/*
		* Try to use the main logbuf even in NMI. But avoid calling console
		* drivers that might have their own locks.

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