From: John Ogness <john.ogness@linutronix.de>
Date: Tue, 19 Sep 2023 14:33:27 +0000
Subject: [PATCH 110/134] printk: nbcon: Use nbcon consoles in
 console_flush_all()
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patches-6.6.7-rt18.tar.xz

Allow nbcon consoles to print messages in the printk() caller
context by integrating them into console_flush_all(). The
write_atomic() callback is used for printing.

Provide nbcon_console_emit_next_record(), which acts as the
nbcon variant of console_emit_next_record(). Call this variant
within console_flush_all() for nbcon consoles. Since nbcon
consoles use their own @nbcon_seq variable to track the next
record to print, this also must be appropriately handled.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 kernel/printk/internal.h |    5 ++++
 kernel/printk/nbcon.c    |   50 +++++++++++++++++++++++++++++++++++++++++++++++
 kernel/printk/printk.c   |   19 +++++++++++++----
 3 files changed, 69 insertions(+), 5 deletions(-)

--- a/kernel/printk/internal.h
+++ b/kernel/printk/internal.h
@@ -71,6 +71,8 @@ void defer_console_output(void);
 
 u16 printk_parse_prefix(const char *text, int *level,
 			enum printk_info_flags *flags);
+void console_lock_spinning_enable(void);
+int console_lock_spinning_disable_and_check(int cookie);
 
 u64 nbcon_seq_read(struct console *con);
 void nbcon_seq_force(struct console *con, u64 seq);
@@ -78,6 +80,7 @@ bool nbcon_alloc(struct console *con);
 void nbcon_init(struct console *con);
 void nbcon_free(struct console *con);
 void nbcon_atomic_flush_all(void);
+bool nbcon_atomic_emit_next_record(struct console *con, bool *handover, int cookie);
 
 /*
  * Check if the given console is currently capable and allowed to print
@@ -133,6 +136,8 @@ static inline bool nbcon_alloc(struct co
 static inline void nbcon_init(struct console *con) { }
 static inline void nbcon_free(struct console *con) { }
 static inline void nbcon_atomic_flush_all(void) { }
+static inline bool nbcon_atomic_emit_next_record(struct console *con, bool *handover,
+						 int cookie) { return false; }
 
 static inline bool console_is_usable(struct console *con, short flags) { return false; }
 
--- a/kernel/printk/nbcon.c
+++ b/kernel/printk/nbcon.c
@@ -532,6 +532,7 @@ static struct printk_buffers panic_nbcon
  * nbcon_context_try_acquire - Try to acquire nbcon console
  * @ctxt:	The context of the caller
  *
+ * Context:	Any context which could not be migrated to another CPU.
  * Return:	True if the console was acquired. False otherwise.
  *
  * If the caller allowed an unsafe hostile takeover, on success the
@@ -961,6 +962,55 @@ static bool nbcon_atomic_emit_one(struct
 }
 
 /**
+ * nbcon_atomic_emit_next_record - Print one record for an nbcon console
+ *					using the write_atomic() callback
+ * @con:	The console to print on
+ * @handover:	Will be set to true if a printk waiter has taken over the
+ *		console_lock, in which case the caller is no longer holding
+ *		both the console_lock and the SRCU read lock. Otherwise it
+ *		is set to false.
+ * @cookie:	The cookie from the SRCU read lock.
+ *
+ * Context:	Any context which could not be migrated to another CPU.
+ * Return:	True if a record could be printed, otherwise false.
+ *
+ * This function is meant to be called by console_flush_all() to print records
+ * on nbcon consoles using the write_atomic() callback. Essentially it is the
+ * nbcon version of console_emit_next_record().
+ */
+bool nbcon_atomic_emit_next_record(struct console *con, bool *handover, int cookie)
+{
+	struct nbcon_write_context wctxt = { };
+	struct nbcon_context *ctxt = &ACCESS_PRIVATE(&wctxt, ctxt);
+	unsigned long driver_flags;
+	bool progress = false;
+	unsigned long flags;
+
+	*handover = false;
+
+	/* Use the same locking order as console_emit_next_record(). */
+	printk_safe_enter_irqsave(flags);
+	console_lock_spinning_enable();
+	stop_critical_timings();
+
+	con->driver_enter(con, &driver_flags);
+	cant_migrate();
+
+	ctxt->console	= con;
+	ctxt->prio	= NBCON_PRIO_NORMAL;
+
+	progress = nbcon_atomic_emit_one(&wctxt);
+
+	con->driver_exit(con, driver_flags);
+
+	start_critical_timings();
+	*handover = console_lock_spinning_disable_and_check(cookie);
+	printk_safe_exit_irqrestore(flags);
+
+	return progress;
+}
+
+/**
  * __nbcon_atomic_flush_all - Flush all nbcon consoles using their
  *					write_atomic() callback
  * @stop_seq:			Flush up until this record
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1872,7 +1872,7 @@ static bool console_waiter;
  * there may be a waiter spinning (like a spinlock). Also it must be
  * ready to hand over the lock at the end of the section.
  */
-static void console_lock_spinning_enable(void)
+void console_lock_spinning_enable(void)
 {
 	/*
 	 * Do not use spinning in panic(). The panic CPU wants to keep the lock.
@@ -1911,7 +1911,7 @@ static void console_lock_spinning_enable
  *
  * Return: 1 if the lock rights were passed, 0 otherwise.
  */
-static int console_lock_spinning_disable_and_check(int cookie)
+int console_lock_spinning_disable_and_check(int cookie)
 {
 	int waiter;
 
@@ -2949,13 +2949,22 @@ static bool console_flush_all(bool do_co
 		cookie = console_srcu_read_lock();
 		for_each_console_srcu(con) {
 			short flags = console_srcu_read_flags(con);
+			u64 printk_seq;
 			bool progress;
 
 			if (!console_is_usable(con, flags))
 				continue;
 			any_usable = true;
 
-			progress = console_emit_next_record(con, handover, cookie);
+			if (flags & CON_NBCON) {
+				progress = nbcon_atomic_emit_next_record(con, handover, cookie);
+
+				printk_seq = nbcon_seq_read(con);
+			} else {
+				progress = console_emit_next_record(con, handover, cookie);
+
+				printk_seq = con->seq;
+			}
 
 			/*
 			 * If a handover has occurred, the SRCU read lock
@@ -2965,8 +2974,8 @@ static bool console_flush_all(bool do_co
 				return false;
 
 			/* Track the next of the highest seq flushed. */
-			if (con->seq > *next_seq)
-				*next_seq = con->seq;
+			if (printk_seq > *next_seq)
+				*next_seq = printk_seq;
 
 			if (!progress)
 				continue;
