Subject: [PATCH 18/48] printk: Let console_is_usable() handle nbcon
From: John Ogness <[email-masked]>
Date: Tue, 12 Sep 2023 13:53:21 +0000

The nbcon consoles use a different printing callback. For nbcon
consoles, check for the write_atomic() callback instead of
write().

Signed-off-by: John Ogness <[email-masked]>
Reviewed-by: Petr Mladek <[email-masked]>
Signed-off-by: Sebastian Andrzej Siewior <[email-masked]>
---
 kernel/printk/internal.h |   11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

Index: linux-6.8.2-rt10/kernel/printk/internal.h
===================================================================
--- linux-6.8.2-rt10.orig/kernel/printk/internal.h
+++ linux-6.8.2-rt10/kernel/printk/internal.h
@@ -87,6 +87,8 @@ void nbcon_free(struct console *con);
 
 /*
  * Check if the given console is currently capable and allowed to print
+ * records. Note that this function does not consider the current context,
+ * which can also play a role in deciding if @con can be used to print
  * records.
  *
  * Requires the console_srcu_read_lock.
@@ -101,8 +103,13 @@ static inline bool console_is_usable(str
 	if ((flags & CON_SUSPENDED))
 		return false;
 
-	if (!con->write)
-		return false;
+	if (flags & CON_NBCON) {
+		if (!con->write_atomic)
+			return false;
+	} else {
+		if (!con->write)
+			return false;
+	}
 
 	/*
 	 * Console drivers may assume that per-cpu resources have been