From: John Ogness <john.ogness@linutronix.de>
Date: Wed, 13 Sep 2023 08:35:23 +0000
Subject: [PATCH 103/134] printk: nbcon: Implement processing in port->lock
 wrapper
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patches-6.6.7-rt18.tar.xz

Currently the port->lock wrappers uart_port_lock(),
uart_port_unlock() (and their variants) only lock/unlock
the spin_lock.

If the port is an nbcon console, the wrappers must also
acquire/release the console and mark the region as unsafe. This
allows general port->lock synchronization to be synchronized
with the nbcon console ownership.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 include/linux/console.h     |    2 +
 include/linux/printk.h      |   13 +++++++
 include/linux/serial_core.h |   18 +++++++++-
 kernel/printk/nbcon.c       |   77 ++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 108 insertions(+), 2 deletions(-)

--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -299,6 +299,7 @@ struct nbcon_write_context {
  * @nbcon_state:	State for nbcon consoles
  * @nbcon_seq:		Sequence number of the next record for nbcon to print
  * @pbufs:		Pointer to nbcon private buffer
+ * @locked_port:	True, if the port lock is locked by nbcon
  */
 struct console {
 	char			name[16];
@@ -325,6 +326,7 @@ struct console {
 	atomic_t		__private nbcon_state;
 	atomic_long_t		__private nbcon_seq;
 	struct printk_buffers	*pbufs;
+	bool			locked_port;
 };
 
 #ifdef CONFIG_LOCKDEP
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -9,6 +9,8 @@
 #include <linux/ratelimit_types.h>
 #include <linux/once_lite.h>
 
+struct uart_port;
+
 extern const char linux_banner[];
 extern const char linux_proc_banner[];
 
@@ -195,6 +197,8 @@ void show_regs_print_info(const char *lo
 extern asmlinkage void dump_stack_lvl(const char *log_lvl) __cold;
 extern asmlinkage void dump_stack(void) __cold;
 void printk_trigger_flush(void);
+extern void nbcon_acquire(struct uart_port *up);
+extern void nbcon_release(struct uart_port *up);
 #else
 static inline __printf(1, 0)
 int vprintk(const char *s, va_list args)
@@ -274,6 +278,15 @@ static inline void dump_stack(void)
 static inline void printk_trigger_flush(void)
 {
 }
+
+static inline void nbcon_acquire(struct uart_port *up)
+{
+}
+
+static inline void nbcon_release(struct uart_port *up)
+{
+}
+
 #endif
 
 #ifdef CONFIG_SMP
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -595,6 +595,7 @@ struct uart_port {
 static inline void uart_port_lock(struct uart_port *up)
 {
 	spin_lock(&up->lock);
+	nbcon_acquire(up);
 }
 
 /**
@@ -604,6 +605,7 @@ static inline void uart_port_lock(struct
 static inline void uart_port_lock_irq(struct uart_port *up)
 {
 	spin_lock_irq(&up->lock);
+	nbcon_acquire(up);
 }
 
 /**
@@ -614,6 +616,7 @@ static inline void uart_port_lock_irq(st
 static inline void uart_port_lock_irqsave(struct uart_port *up, unsigned long *flags)
 {
 	spin_lock_irqsave(&up->lock, *flags);
+	nbcon_acquire(up);
 }
 
 /**
@@ -624,7 +627,11 @@ static inline void uart_port_lock_irqsav
  */
 static inline bool uart_port_trylock(struct uart_port *up)
 {
-	return spin_trylock(&up->lock);
+	if (!spin_trylock(&up->lock))
+		return false;
+
+	nbcon_acquire(up);
+	return true;
 }
 
 /**
@@ -636,7 +643,11 @@ static inline bool uart_port_trylock(str
  */
 static inline bool uart_port_trylock_irqsave(struct uart_port *up, unsigned long *flags)
 {
-	return spin_trylock_irqsave(&up->lock, *flags);
+	if (!spin_trylock_irqsave(&up->lock, *flags))
+		return false;
+
+	nbcon_acquire(up);
+	return true;
 }
 
 /**
@@ -645,6 +656,7 @@ static inline bool uart_port_trylock_irq
  */
 static inline void uart_port_unlock(struct uart_port *up)
 {
+	nbcon_release(up);
 	spin_unlock(&up->lock);
 }
 
@@ -654,6 +666,7 @@ static inline void uart_port_unlock(stru
  */
 static inline void uart_port_unlock_irq(struct uart_port *up)
 {
+	nbcon_release(up);
 	spin_unlock_irq(&up->lock);
 }
 
@@ -664,6 +677,7 @@ static inline void uart_port_unlock_irq(
  */
 static inline void uart_port_unlock_irqrestore(struct uart_port *up, unsigned long flags)
 {
+	nbcon_release(up);
 	spin_unlock_irqrestore(&up->lock, flags);
 }
 
--- a/kernel/printk/nbcon.c
+++ b/kernel/printk/nbcon.c
@@ -6,6 +6,7 @@
 #include <linux/console.h>
 #include <linux/delay.h>
 #include <linux/slab.h>
+#include <linux/serial_core.h>
 #include "internal.h"
 /*
  * Printk console printing implementation for consoles which does not depend
@@ -995,3 +996,79 @@ void nbcon_free(struct console *con)
 
 	con->pbufs = NULL;
 }
+
+static inline bool uart_is_nbcon(struct uart_port *up)
+{
+	int cookie;
+	bool ret;
+
+	if (!uart_console(up))
+		return false;
+
+	cookie = console_srcu_read_lock();
+	ret = (console_srcu_read_flags(up->cons) & CON_NBCON);
+	console_srcu_read_unlock(cookie);
+	return ret;
+}
+
+/**
+ * nbcon_acquire - The second half of the port locking wrapper
+ * @up:		The uart port whose @lock was locked
+ *
+ * The uart_port_lock() wrappers will first lock the spin_lock @up->lock.
+ * Then this function is called to implement nbcon-specific processing.
+ *
+ * If @up is an nbcon console, this console will be acquired and marked as
+ * unsafe. Otherwise this function does nothing.
+ */
+void nbcon_acquire(struct uart_port *up)
+{
+	struct console *con = up->cons;
+	struct nbcon_context ctxt;
+
+	if (!uart_is_nbcon(up))
+		return;
+
+	WARN_ON_ONCE(con->locked_port);
+
+	do {
+		do {
+			memset(&ctxt, 0, sizeof(ctxt));
+			ctxt.console	= con;
+			ctxt.prio	= NBCON_PRIO_NORMAL;
+		} while (!nbcon_context_try_acquire(&ctxt));
+
+	} while (!nbcon_context_enter_unsafe(&ctxt));
+
+	con->locked_port = true;
+}
+EXPORT_SYMBOL_GPL(nbcon_acquire);
+
+/**
+ * nbcon_release - The first half of the port unlocking wrapper
+ * @up:		The uart port whose @lock is about to be unlocked
+ *
+ * The uart_port_unlock() wrappers will first call this function to implement
+ * nbcon-specific processing. Then afterwards the uart_port_unlock() wrappers
+ * will unlock the spin_lock @up->lock.
+ *
+ * If @up is an nbcon console, the console will be marked as safe and
+ * released. Otherwise this function does nothing.
+ */
+void nbcon_release(struct uart_port *up)
+{
+	struct console *con = up->cons;
+	struct nbcon_context ctxt = {
+		.console	= con,
+		.prio		= NBCON_PRIO_NORMAL,
+	};
+
+	if (!con->locked_port)
+		return;
+
+	if (nbcon_context_exit_unsafe(&ctxt))
+		nbcon_context_release(&ctxt);
+
+	con->locked_port = false;
+}
+EXPORT_SYMBOL_GPL(nbcon_release);
