linux-kernel - [PATCH] kgdb: Make "kgdbcon" work properly with "kgdb

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Message-Id: <20200630151422.1.I4aa062751ff5e281f5116655c976dff545c09a46@changeid>
Date:   Tue, 30 Jun 2020 15:14:38 -0700
From:   Douglas Anderson <dianders@...omium.org>
To:     Daniel Thompson <daniel.thompson@...aro.org>
Cc:     Sumit Garg <sumit.garg@...aro.org>,
        Douglas Anderson <dianders@...omium.org>,
        Jason Wessel <jason.wessel@...driver.com>,
        kgdb-bugreport@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: [PATCH] kgdb: Make "kgdbcon" work properly with "kgdb_earlycon"

On my system the kernel processes the "kgdb_earlycon" parameter before
the "kgdbcon" parameter.  When we setup "kgdb_earlycon" we'll end up
in kgdb_register_callbacks() and "kgdb_use_con" won't have been set
yet so we'll never get around to starting "kgdbcon".  Let's remedy
this by detecting that the IO module was already registered when
setting "kgdb_use_con" and registering the console then.

As part of this, to avoid pre-declaring things, move the handling of
the "kgdbcon" further down in the file.

Signed-off-by: Douglas Anderson <dianders@...omium.org>
---

 kernel/debug/debug_core.c | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c
index 9e5934780f41..03d5b17347da 100644
--- a/kernel/debug/debug_core.c
+++ b/kernel/debug/debug_core.c
@@ -94,14 +94,6 @@ int dbg_switch_cpu;
 /* Use kdb or gdbserver mode */
 int dbg_kdb_mode = 1;
 
-static int __init opt_kgdb_con(char *str)
-{
-	kgdb_use_con = 1;
-	return 0;
-}
-
-early_param("kgdbcon", opt_kgdb_con);
-
 module_param(kgdb_use_con, int, 0644);
 module_param(kgdbreboot, int, 0644);
 
@@ -920,6 +912,20 @@ static struct console kgdbcons = {
 	.index		= -1,
 };
 
+static int __init opt_kgdb_con(char *str)
+{
+	kgdb_use_con = 1;
+
+	if (kgdb_io_module_registered && !kgdb_con_registered) {
+		register_console(&kgdbcons);
+		kgdb_con_registered = 1;
+	}
+
+	return 0;
+}
+
+early_param("kgdbcon", opt_kgdb_con);
+
 #ifdef CONFIG_MAGIC_SYSRQ
 static void sysrq_handle_dbg(int key)
 {
-- 
2.27.0.212.ge8ba1cc988-goog