Subject: [PATCH 13/24] printk: nobkl: Add write context storage for atomic writes
From: Thomas Gleixner <[email-masked]>
Date: Sun, 11 Sep 2022 00:28:13 +0200

The number of consoles is unknown at compile time and allocating
write contexts on stack in emergency/panic situations is not desired
either.

Allocate a write context array (one for each priority level) along
with the per CPU output buffers, thus allowing atomic contexts on
multiple CPUs and priority levels to execute simultaneously without
clobbering each other's write context.

Co-developed-by: John Ogness <[email-masked]>
Signed-off-by: John Ogness <[email-masked]>
Signed-off-by: Thomas Gleixner (Intel) <[email-masked]>
Signed-off-by: Sebastian Andrzej Siewior <[email-masked]>
---
 include/linux/console.h  |    2 ++
 kernel/printk/internal.h |    5 +++++
 2 files changed, 7 insertions(+)

Index: linux-6.3.0-rt11/include/linux/console.h
===================================================================
--- linux-6.3.0-rt11.orig/include/linux/console.h
+++ linux-6.3.0-rt11/include/linux/console.h
@@ -223,6 +223,7 @@ struct cons_state {
  * @CONS_PRIO_NORMAL:		Regular printk
  * @CONS_PRIO_EMERGENCY:	Emergency output (WARN/OOPS...)
  * @CONS_PRIO_PANIC:		Panic output
+ * @CONS_PRIO_MAX:		The number of priority levels
  *
  * Emergency output can carefully takeover the console even without consent
  * of the owner, ideally only when @cons_state::unsafe is not set. Panic
@@ -235,6 +236,7 @@ enum cons_prio {
 	CONS_PRIO_NORMAL,
 	CONS_PRIO_EMERGENCY,
 	CONS_PRIO_PANIC,
+	CONS_PRIO_MAX,
 };
 
 struct console;
Index: linux-6.3.0-rt11/kernel/printk/internal.h
===================================================================
--- linux-6.3.0-rt11.orig/kernel/printk/internal.h
+++ linux-6.3.0-rt11/kernel/printk/internal.h
@@ -182,11 +182,16 @@ struct printk_message {
 
 /**
  * struct cons_context_data - console context data
+ * @wctxt:		Write context per priority level
  * @pbufs:		Buffer for storing the text
  *
  * Used for early boot and for per CPU data.
+ *
+ * The write contexts are allocated to avoid having them on stack, e.g. in
+ * warn() or panic().
  */
 struct cons_context_data {
+	struct cons_write_context	wctxt[CONS_PRIO_MAX];
 	struct printk_buffers		pbufs;
 };