linux-kernel - [PATCH] printk/kdb: Redirect printk messages into kdb in any context

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Message-ID: <20200515085021.GS17734@linux-b0ei>
Date:   Fri, 15 May 2020 10:50:21 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Sumit Garg <sumit.garg@...aro.org>
Cc:     Daniel Thompson <daniel.thompson@...aro.org>,
        Jason Wessel <jason.wessel@...driver.com>,
        Douglas Anderson <dianders@...omium.org>,
        kgdb-bugreport@...ts.sourceforge.net,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        John Ogness <john.ogness@...utronix.de>,
        Petr Mladek <pmladek@...e.com>
Subject: [PATCH] printk/kdb: Redirect printk messages into kdb in any context

kdb is able to stop kernel even in NMI context where printk() is redirected
to the printk_safe() lockless variant. Move the check and redirect to kdb
even in this case.

Reported-by: Sumit Garg <sumit.garg@...aro.org>
Tested-by: Sumit Garg <sumit.garg@...aro.org>
Signed-off-by: Petr Mladek <pmladek@...e.com>
---
Sending as proper patch for review.
Adding Sergey into CC and John into CC.

kernel/printk/printk.c      | 14 +-------------
 kernel/printk/printk_safe.c |  7 +++++++
 2 files changed, 8 insertions(+), 13 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 9a9b6156270b..63a1aa377cd9 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>
@@ -2036,18 +2035,7 @@ 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);
 
diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c
index d9a659a686f3..7ccb821d0bfe 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 @@ 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.
-- 
2.26.1