[PATCH printk v2 08/26] printk: nbcon: Implement processing in port->lock wrapper

[John Ogness]

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.

Add a flag to struct uart_port to track nbcon console ownership.

Signed-off-by: John Ogness <john.ogness@xxxxxxxxxxxxx>
---
 drivers/tty/serial/8250/8250_port.c |  1 +
 include/linux/printk.h              | 13 +++++
 include/linux/serial_core.h         | 19 ++++++-
 kernel/printk/nbcon.c               | 77 +++++++++++++++++++++++++++++
 4 files changed, 108 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 141627370aab..16e2705b4867 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -3284,6 +3284,7 @@ void serial8250_init_port(struct uart_8250_port *up)
 	struct uart_port *port = &up->port;
 
 	spin_lock_init(&port->lock);
+	port->nbcon_locked_port = false;
 	port->ctrl_id = 0;
 	port->pm = NULL;
 	port->ops = &serial8250_pops;
diff --git a/include/linux/printk.h b/include/linux/printk.h
index 8d5c5588eec9..ef57a4d93ae2 100644
--- 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 *log_lvl);
 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 uart_nbcon_acquire(struct uart_port *up);
+extern void uart_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 uart_nbcon_acquire(struct uart_port *up)
+{
+}
+
+static inline void uart_nbcon_release(struct uart_port *up)
+{
+}
+
 #endif
 
 bool this_cpu_in_panic(void);
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index 89f7b6c63598..d4b93d721715 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -488,6 +488,7 @@ struct uart_port {
 	struct uart_icount	icount;			/* statistics */
 
 	struct console		*cons;			/* struct console, if any */
+	bool			nbcon_locked_port;	/* True, if the port is locked by nbcon */
 	/* flags must be updated while holding port mutex */
 	upf_t			flags;
 
@@ -595,6 +596,7 @@ struct uart_port {
 static inline void uart_port_lock(struct uart_port *up)
 {
 	spin_lock(&up->lock);
+	uart_nbcon_acquire(up);
 }
 
 /**
@@ -604,6 +606,7 @@ static inline void uart_port_lock(struct uart_port *up)
 static inline void uart_port_lock_irq(struct uart_port *up)
 {
 	spin_lock_irq(&up->lock);
+	uart_nbcon_acquire(up);
 }
 
 /**
@@ -614,6 +617,7 @@ static inline void uart_port_lock_irq(struct uart_port *up)
 static inline void uart_port_lock_irqsave(struct uart_port *up, unsigned long *flags)
 {
 	spin_lock_irqsave(&up->lock, *flags);
+	uart_nbcon_acquire(up);
 }
 
 /**
@@ -624,7 +628,11 @@ static inline void uart_port_lock_irqsave(struct uart_port *up, unsigned long *f
  */
 static inline bool uart_port_trylock(struct uart_port *up)
 {
-	return spin_trylock(&up->lock);
+	if (!spin_trylock(&up->lock))
+		return false;
+
+	uart_nbcon_acquire(up);
+	return true;
 }
 
 /**
@@ -636,7 +644,11 @@ static inline bool uart_port_trylock(struct uart_port *up)
  */
 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;
+
+	uart_nbcon_acquire(up);
+	return true;
 }
 
 /**
@@ -645,6 +657,7 @@ static inline bool uart_port_trylock_irqsave(struct uart_port *up, unsigned long
  */
 static inline void uart_port_unlock(struct uart_port *up)
 {
+	uart_nbcon_release(up);
 	spin_unlock(&up->lock);
 }
 
@@ -654,6 +667,7 @@ static inline void uart_port_unlock(struct uart_port *up)
  */
 static inline void uart_port_unlock_irq(struct uart_port *up)
 {
+	uart_nbcon_release(up);
 	spin_unlock_irq(&up->lock);
 }
 
@@ -664,6 +678,7 @@ static inline void uart_port_unlock_irq(struct uart_port *up)
  */
 static inline void uart_port_unlock_irqrestore(struct uart_port *up, unsigned long flags)
 {
+	uart_nbcon_release(up);
 	spin_unlock_irqrestore(&up->lock, flags);
 }
 
diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c
index 8ecd76aa22e6..02e8fdc1ea43 100644
--- 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;
+}
+
+/**
+ * uart_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 uart_nbcon_acquire(struct uart_port *up)
+{
+	struct console *con = up->cons;
+	struct nbcon_context ctxt;
+
+	if (!uart_is_nbcon(up))
+		return;
+
+	WARN_ON_ONCE(up->nbcon_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));
+
+	up->nbcon_locked_port = true;
+}
+EXPORT_SYMBOL_GPL(uart_nbcon_acquire);
+
+/**
+ * uart_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 uart_nbcon_release(struct uart_port *up)
+{
+	struct console *con = up->cons;
+	struct nbcon_context ctxt = {
+		.console	= con,
+		.prio		= NBCON_PRIO_NORMAL,
+	};
+
+	if (!up->nbcon_locked_port)
+		return;
+
+	if (nbcon_context_exit_unsafe(&ctxt))
+		nbcon_context_release(&ctxt);
+
+	up->nbcon_locked_port = false;
+}
+EXPORT_SYMBOL_GPL(uart_nbcon_release);
-- 
2.39.2