From b7ce10dc9059ee9a08524df4c62247d29bc4b14d Mon Sep 17 00:00:00 2001
From: John Ogness <john.ogness@linutronix.de>
Date: Fri, 19 Mar 2021 14:57:31 +0100
Subject: [PATCH 006/158] kdb: only use atomic consoles for output mirroring

Currently kdb uses the @oops_in_progress hack to mirror kdb output
to all active consoles from NMI context. Ignoring locks is unsafe.
Now that an NMI-safe atomic interfaces is available for consoles,
use that interface to mirror kdb output.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 kernel/debug/kdb/kdb_io.c |   18 ++++++------------
 1 file changed, 6 insertions(+), 12 deletions(-)

Index: linux-5.15/kernel/debug/kdb/kdb_io.c
===================================================================
--- linux-5.15.orig/kernel/debug/kdb/kdb_io.c
+++ linux-5.15/kernel/debug/kdb/kdb_io.c
@@ -559,23 +559,17 @@ static void kdb_msg_write(const char *ms
 		cp++;
 	}
 
+	/* mirror output on atomic consoles */
 	for_each_console(c) {
 		if (!(c->flags & CON_ENABLED))
 			continue;
 		if (c == dbg_io_ops->cons)
 			continue;
-		/*
-		 * Set oops_in_progress to encourage the console drivers to
-		 * disregard their internal spin locks: in the current calling
-		 * context the risk of deadlock is a bigger problem than risks
-		 * due to re-entering the console driver. We operate directly on
-		 * oops_in_progress rather than using bust_spinlocks() because
-		 * the calls bust_spinlocks() makes on exit are not appropriate
-		 * for this calling context.
-		 */
-		++oops_in_progress;
-		c->write(c, msg, msg_len);
-		--oops_in_progress;
+
+		if (!c->write_atomic)
+			continue;
+		c->write_atomic(c, msg, msg_len);
+
 		touch_nmi_watchdog();
 	}
 }