linux-kernel - [patch RFC 27/29] printk: Add write context storage for atomic writes

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Date:   Sun, 11 Sep 2022 00:28:13 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     John Ogness <john.ogness@...utronix.de>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Daniel Vetter <daniel@...ll.ch>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Helge Deller <deller@....de>,
        Jason Wessel <jason.wessel@...driver.com>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        John Ogness <jogness@...utronix.de>
Subject: [patch RFC 27/29] printk: Add write context storage for atomic writes

From: John Ogness <jogness@...utronix.de>

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.

Signed-off-by: John Ogness <jogness@...utronix.de>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 include/linux/console.h |    7 +++++++
 1 file changed, 7 insertions(+)

--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -253,6 +253,7 @@ struct cons_outbuf_desc {
  * @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
@@ -265,6 +266,7 @@ enum cons_prio {
 	CONS_PRIO_NORMAL,
 	CONS_PRIO_EMERGENCY,
 	CONS_PRIO_PANIC,
+	CONS_PRIO_MAX,
 };
 
 struct console;
@@ -327,12 +329,17 @@ struct cons_write_context {
 
 /**
  * struct cons_context_data - console context data
+ * @wctxt:		Write context per priority level
  * @txtbuf:		Buffer for storing the text
  *
  * Used for early boot embedded into struct console 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 cons_text_buf		txtbuf;
 };