linux-kernel - [PATCH printk v3 7/7] printk: nbcon: Add functions for drivers to mark unsafe regions

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Message-Id: <20230903150539.245076-8-john.ogness@linutronix.de>
Date:   Sun,  3 Sep 2023 17:11:39 +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,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: [PATCH printk v3 7/7] printk: nbcon: Add functions for drivers to mark unsafe regions

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

For the write_atomic callback, the console driver may have unsafe
regions that need to be appropriately marked. Provide functions
that accept the nbcon_write_context struct to allow for the driver
to enter and exit unsafe regions.

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>
---
 include/linux/console.h |  4 ++++
 kernel/printk/nbcon.c   | 40 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 44 insertions(+)

diff --git a/include/linux/console.h b/include/linux/console.h
index 8d0a309b5286..b3ea9ea66a38 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -459,8 +459,12 @@ static inline bool console_is_registered(const struct console *con)
 
 #ifdef CONFIG_PRINTK
 extern bool nbcon_can_proceed(struct nbcon_write_context *wctxt);
+extern bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt);
+extern bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt);
 #else
 static inline bool nbcon_can_proceed(struct nbcon_write_context *wctxt) { return false; }
+static inline bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt) { return false; }
+static inline bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt) { return false; }
 #endif
 
 extern int console_set_on_cmdline;
diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c
index 1a3df603111d..74f9c33201ae 100644
--- a/kernel/printk/nbcon.c
+++ b/kernel/printk/nbcon.c
@@ -756,6 +756,46 @@ static bool nbcon_context_update_unsafe(struct nbcon_context *ctxt, bool unsafe)
 	return nbcon_context_can_proceed(ctxt, &cur);
 }
 
+/**
+ * nbcon_enter_unsafe - Enter an unsafe region in the driver
+ * @wctxt:	The write context that was handed to the write function
+ *
+ * Return:	True if this context still owns the console. False if
+ *		ownership was handed over or taken.
+ *
+ * When this function returns false then the calling context no longer owns
+ * the console and is no longer allowed to go forward. In this case it must
+ * back out immediately and carefully. The buffer content is also no longer
+ * trusted since it no longer belongs to the calling context.
+ */
+bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt)
+{
+	struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt);
+
+	return nbcon_context_update_unsafe(ctxt, true);
+}
+EXPORT_SYMBOL_GPL(nbcon_enter_unsafe);
+
+/**
+ * nbcon_exit_unsafe - Exit an unsafe region in the driver
+ * @wctxt:	The write context that was handed to the write function
+ *
+ * Return:	True if this context still owns the console. False if
+ *		ownership was handed over or taken.
+ *
+ * When this function returns false then the calling context no longer owns
+ * the console and is no longer allowed to go forward. In this case it must
+ * back out immediately and carefully. The buffer content is also no longer
+ * trusted since it no longer belongs to the calling context.
+ */
+bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt)
+{
+	struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt);
+
+	return nbcon_context_update_unsafe(ctxt, false);
+}
+EXPORT_SYMBOL_GPL(nbcon_exit_unsafe);
+
 /**
  * nbcon_emit_next_record - Emit a record in the acquired context
  * @wctxt:	The write context that will be handed to the write function
-- 
2.39.2