linux-kernel - [PATCH printk v2 1/2] printk: Allow printk_trigger

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Message-ID: <20251113160351.113031-2-john.ogness@linutronix.de>
Date: Thu, 13 Nov 2025 17:09:47 +0106
From: John Ogness <john.ogness@...utronix.de>
To: Petr Mladek <pmladek@...e.com>
Cc: Sergey Senozhatsky <senozhatsky@...omium.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Sherry Sun <sherry.sun@....com>,
	Jacky Bai <ping.bai@....com>,
	Jon Hunter <jonathanh@...dia.com>,
	Thierry Reding <thierry.reding@...il.com>,
	Derek Barbosa <debarbos@...hat.com>,
	linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: [PATCH printk v2 1/2] printk: Allow printk_trigger_flush() to flush all types

Currently printk_trigger_flush() only triggers legacy offloaded
flushing, even if that may not be the appropriate method to flush
for currently registered consoles. (The function predates the
NBCON consoles.)

Since commit 6690d6b52726 ("printk: Add helper for flush type
logic") there is printk_get_console_flush_type(), which also
considers NBCON consoles and reports all the methods of flushing
appropriate based on the system state and consoles available.

Update printk_trigger_flush() to use
printk_get_console_flush_type() to appropriately flush registered
consoles.

Suggested-by: Petr Mladek <pmladek@...e.com>
Signed-off-by: John Ogness <john.ogness@...utronix.de>
---
 kernel/printk/nbcon.c  |  2 +-
 kernel/printk/printk.c | 23 ++++++++++++++++++++++-
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c
index 558ef31779760..73f315fd97a3e 100644
--- a/kernel/printk/nbcon.c
+++ b/kernel/printk/nbcon.c
@@ -1849,7 +1849,7 @@ void nbcon_device_release(struct console *con)
 			if (console_trylock())
 				console_unlock();
 		} else if (ft.legacy_offload) {
-			printk_trigger_flush();
+			defer_console_output();
 		}
 	}
 	console_srcu_read_unlock(cookie);
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 5aee9ffb16b9a..dc89239cf1b58 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -4567,9 +4567,30 @@ void defer_console_output(void)
 	__wake_up_klogd(PRINTK_PENDING_WAKEUP | PRINTK_PENDING_OUTPUT);
 }
 
+/**
+ * printk_trigger_flush - Attempt to flush printk buffer to consoles.
+ *
+ * If possible, flush the printk buffer to all consoles in the caller's
+ * context. If offloading is available, trigger deferred printing.
+ *
+ * This is best effort. Depending on the system state, console states,
+ * and caller context, no actual flushing may result from this call.
+ */
 void printk_trigger_flush(void)
 {
-	defer_console_output();
+	struct console_flush_type ft;
+
+	printk_get_console_flush_type(&ft);
+	if (ft.nbcon_atomic)
+		nbcon_atomic_flush_pending();
+	if (ft.nbcon_offload)
+		nbcon_kthreads_wake();
+	if (ft.legacy_direct) {
+		if (console_trylock())
+			console_unlock();
+	}
+	if (ft.legacy_offload)
+		defer_console_output();
 }
 
 int vprintk_deferred(const char *fmt, va_list args)
-- 
2.47.3