printk/kdb: Redirect printk messages into kdb in any context
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
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 9fdd6a42..2167bb5 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -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 @@
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);
diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c
index d9a659a..7ccb821 100644
--- a/kernel/printk/printk_safe.c
+++ b/kernel/printk/printk_safe.c
@@ -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 @@
__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.
