From 81647717a400454f8891e60eab85ab5c809898f3 Mon Sep 17 00:00:00 2001
From: John Ogness <john.ogness@linutronix.de>
Date: Mon, 7 Feb 2022 15:53:45 +0106
Subject: [PATCH] printk: use percpu flag instead of cpu_online()

References: SLE Realtime Extension
Patch-mainline: Queued in subsystem maintainer repository
Git-commit: c8fe75f61199835699bf4361b3f6ec00512f0a3b
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git

The CON_ANYTIME console flag is used to label consoles that will
work correctly before percpu resources are allocated. To check
the condition, cpu_online(raw_smp_processor_id()) was used.
However, this is odd because CPUs can go offline at a later point.
Also, the function is forced to use the raw_ variant because
migration is not disabled.

Since commit ab6f762f0f53 ("printk: queue wake_up_klogd irq_work
only if per-CPU areas are ready") there is a variable to identify
if percpu resources have been allocated. Use that variable instead
of cpu_online(raw_smp_processor_id()).

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
 include/linux/console.h | 2 +-
 kernel/printk/printk.c  | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/linux/console.h b/include/linux/console.h
index a97f277cfdfa..1987dcd06be7 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -133,7 +133,7 @@ static inline int con_debug_leave(void)
 #define CON_CONSDEV	(2) /* Preferred console, /dev/console */
 #define CON_ENABLED	(4)
 #define CON_BOOT	(8)
-#define CON_ANYTIME	(16) /* Safe to call when cpu is offline */
+#define CON_ANYTIME	(16) /* Safe to call before per-cpu resources ready */
 #define CON_BRL		(32) /* Used for a braille device */
 #define CON_EXTENDED	(64) /* Use the extended output format a la /dev/kmsg */
 
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 8bdf3286ccb9..74c0862e2e93 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2604,11 +2604,11 @@ static int have_callable_console(void)
  *
  * Console drivers may assume that per-cpu resources have been allocated. So
  * unless they're explicitly marked as being able to cope (CON_ANYTIME) don't
- * call them until this CPU is officially up.
+ * call them until per-cpu resources have been allocated.
  */
 static inline int can_use_console(void)
 {
-	return cpu_online(raw_smp_processor_id()) || have_callable_console();
+	return (printk_percpu_data_ready() || have_callable_console());
 }
 
 /**