1 files changed, 209 insertions, 0 deletions
diff --git a/debian/patches-rt/0020-printk-nbcon-Use-nbcon-consoles-in-console_flush_all.patch b/debian/patches-rt/0020-printk-nbcon-Use-nbcon-consoles-in-console_flush_all.patch
new file mode 100644
index 0000000000..3507ff2aa2
--- /dev/null
+++ b/debian/patches-rt/0020-printk-nbcon-Use-nbcon-consoles-in-console_flush_all.patch
@@ -0,0 +1,209 @@
+From: John Ogness <john.ogness@linutronix.de>
+Date: Tue, 19 Sep 2023 14:33:27 +0000
+Subject: [PATCH 20/46] printk: nbcon: Use nbcon consoles in
+ console_flush_all()
+Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.9/older/patches-6.9-rt5.tar.xz
+
+Allow nbcon consoles to print messages in the legacy printk()
+caller context (printing via unlock) by integrating them into
+console_flush_all(). The write_atomic() callback is used for
+printing.
+
+Provide nbcon_legacy_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 in
+console_flush_all().
+
+Note that the legacy printing logic uses @handover to detect
+handovers for printing all consoles. For nbcon consoles,
+handovers/takeovers occur on a per-console basis and thus do
+not cause the console_flush_all() loop to abort.
+
+Signed-off-by: John Ogness <john.ogness@linutronix.de>
+Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+---
+ kernel/printk/internal.h |    6 +++
+ kernel/printk/nbcon.c    |   87 +++++++++++++++++++++++++++++++++++++++++++++++
+ kernel/printk/printk.c   |   17 ++++++---
+ 3 files changed, 105 insertions(+), 5 deletions(-)
+
+--- a/kernel/printk/internal.h
++++ b/kernel/printk/internal.h
+@@ -78,6 +78,8 @@ 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);
+@@ -86,6 +88,8 @@ void nbcon_init(struct console *con, u64
+ void nbcon_free(struct console *con);
+ enum nbcon_prio nbcon_get_default_prio(void);
+ void nbcon_atomic_flush_pending(void);
++bool nbcon_legacy_emit_next_record(struct console *con, bool *handover,
++				   int cookie);
+ 
+ /*
+  * Check if the given console is currently capable and allowed to print
+@@ -142,6 +146,8 @@ static inline void nbcon_init(struct con
+ static inline void nbcon_free(struct console *con) { }
+ static inline enum nbcon_prio nbcon_get_default_prio(void) { return NBCON_PRIO_NONE; }
+ static inline void nbcon_atomic_flush_pending(void) { }
++static inline bool nbcon_legacy_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
+@@ -953,6 +953,93 @@ enum nbcon_prio nbcon_get_default_prio(v
+ }
+ 
+ /*
++ * nbcon_atomic_emit_one - Print one record for an nbcon console using the
++ *				write_atomic() callback
++ * @wctxt:	An initialized write context struct to use for this context
++ *
++ * Return:	True, when a record has been printed and there are still
++ *		pending records. The caller might want to continue flushing.
++ *
++ *		False, when there is no pending record, or when the console
++ *		context cannot be acquired, or the ownership has been lost.
++ *		The caller should give up. Either the job is done, cannot be
++ *		done, or will be handled by the owning context.
++ *
++ * This is an internal helper to handle the locking of the console before
++ * calling nbcon_emit_next_record().
++ */
++static bool nbcon_atomic_emit_one(struct nbcon_write_context *wctxt)
++{
++	struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt);
++
++	if (!nbcon_context_try_acquire(ctxt))
++		return false;
++
++	/*
++	 * nbcon_emit_next_record() returns false when the console was
++	 * handed over or taken over. In both cases the context is no
++	 * longer valid.
++	 *
++	 * The higher priority printing context takes over responsibility
++	 * to print the pending records.
++	 */
++	if (!nbcon_emit_next_record(wctxt))
++		return false;
++
++	nbcon_context_release(ctxt);
++
++	return ctxt->backlog;
++}
++
++/**
++ * nbcon_legacy_emit_next_record - Print one record for an nbcon console
++ *					in legacy contexts
++ * @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 except NMI.
++ * Return:	True, when a record has been printed and there are still
++ *		pending records. The caller might want to continue flushing.
++ *
++ *		False, when there is no pending record, or when the console
++ *		context cannot be acquired, or the ownership has been lost.
++ *		The caller should give up. Either the job is done, cannot be
++ *		done, or will be handled by the owning context.
++ *
++ * This function is meant to be called by console_flush_all() to print records
++ * on nbcon consoles from legacy context (printing via console unlocking).
++ * Essentially it is the nbcon version of console_emit_next_record().
++ */
++bool nbcon_legacy_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 flags;
++	bool progress;
++
++	/* Use the same procedure as console_emit_next_record(). */
++	printk_safe_enter_irqsave(flags);
++	console_lock_spinning_enable();
++	stop_critical_timings();
++
++	ctxt->console	= con;
++	ctxt->prio	= nbcon_get_default_prio();
++
++	progress = nbcon_atomic_emit_one(&wctxt);
++
++	start_critical_timings();
++	*handover = console_lock_spinning_disable_and_check(cookie);
++	printk_safe_exit_irqrestore(flags);
++
++	return progress;
++}
++
++/**
+  * __nbcon_atomic_flush_pending_con - Flush specified nbcon console using its
+  *					write_atomic() callback
+  * @con:			The nbcon console to flush
+--- a/kernel/printk/printk.c
++++ b/kernel/printk/printk.c
+@@ -1860,7 +1860,7 @@ 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.
+@@ -1899,7 +1899,7 @@ 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;
+ 
+@@ -2951,13 +2951,20 @@ 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_legacy_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
+@@ -2967,8 +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;