linux-kernel - [PATCH printk v2 06/11] printk: nbcon: Wire up nbcon console atomic flushing

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Message-Id: <20230919230856.661435-7-john.ogness@linutronix.de>
Date:   Wed, 20 Sep 2023 01:14:51 +0206
From:   John Ogness <john.ogness@...utronix.de>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org
Subject: [PATCH printk v2 06/11] printk: nbcon: Wire up nbcon console atomic flushing

From: Thomas Gleixner <tglx@...utronix.de>

Perform nbcon console atomic flushing at key call sites:

nbcon_atomic_exit() - When exiting from the outermost atomic
	printing section. If the priority was NBCON_PRIO_PANIC,
	attempt a second flush allowing unsafe hostile
	takeovers.

console_flush_on_panic() - Called from several call sites to
	trigger ringbuffer dumping in an urgent situation.

console_flush_on_panic() - Typically the panic() function will
	take care of atomic flushing the nbcon consoles on
	panic. However, there are several users of
	console_flush_on_panic() outside of panic().

printk_trigger_flush() - Used in urgent situations to trigger a
	dump in an irq_work context. However, the atomic
	flushing part happens in the calling context since an
	alternative context is not required.

Co-developed-by: John Ogness <john.ogness@...utronix.de>
Signed-off-by: John Ogness <john.ogness@...utronix.de>
Signed-off-by: Thomas Gleixner (Intel) <tglx@...utronix.de>
---
 kernel/printk/nbcon.c  | 10 ++++++++++
 kernel/printk/printk.c |  6 ++++++
 2 files changed, 16 insertions(+)

diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c
index 2a9ff18fc78c..82e6a1678363 100644
--- a/kernel/printk/nbcon.c
+++ b/kernel/printk/nbcon.c
@@ -1092,6 +1092,11 @@ void nbcon_atomic_flush_all(void)
  * Return:	The previous priority that needs to be fed into
  *		the corresponding nbcon_atomic_exit()
  * Context:	Any context. Disables migration.
+ *
+ * When within an atomic printing section, no atomic printing occurs. This
+ * is to allow all emergency messages to be dumped into the ringbuffer before
+ * flushing the ringbuffer. The actual atomic printing occurs when exiting
+ * the outermost atomic printing section.
  */
 enum nbcon_prio nbcon_atomic_enter(enum nbcon_prio prio)
 {
@@ -1130,8 +1135,13 @@ void nbcon_atomic_exit(enum nbcon_prio prio, enum nbcon_prio prev_prio)
 {
 	struct nbcon_cpu_state *cpu_state;
 
+	__nbcon_atomic_flush_all(false);
+
 	cpu_state = nbcon_get_cpu_state();
 
+	if (cpu_state->prio == NBCON_PRIO_PANIC)
+		__nbcon_atomic_flush_all(true);
+
 	/*
 	 * Undo the nesting of nbcon_atomic_enter() at the CPU state
 	 * priority.
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 6ef33cefa4d0..419c0fabc481 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3159,6 +3159,8 @@ void console_flush_on_panic(enum con_flush_mode mode)
 		console_srcu_read_unlock(cookie);
 	}
 
+	nbcon_atomic_flush_all();
+
 	console_flush_all(false, &next_seq, &handover);
 }
 
@@ -3903,6 +3905,10 @@ void defer_console_output(void)
 
 void printk_trigger_flush(void)
 {
+	migrate_disable();
+	nbcon_atomic_flush_all();
+	migrate_enable();
+
 	defer_console_output();
 }
 
-- 
2.39.2