[PATCH printk v5 12/30] serial: core: Implement processing in port->lock wrapper

John Ogness
2024-05-02T21:38:50Z

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.

Note that __uart_port_using_nbcon() relies on the port->lock
being held while a console is added and removed from the
console list (i.e. all uart nbcon drivers *must* take the
port->lock in their device_lock() callbacks).

Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
include/linux/serial_core.h | 82 ++++++++++++++++++++++++++++++++++++-
1 file changed, 80 insertions(+), 2 deletions(-)

diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index 038693774f21..a2f307dce221 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -12,6 +12,8 @@
#include <linux/console.h>
#include <linux/interrupt.h>
#include <linux/circ_buf.h>
+#include <linux/lockdep.h>
+#include <linux/printk.h>
#include <linux/spinlock.h>
#include <linux/sched.h>
#include <linux/tty.h>
@@ -623,6 +625,60 @@ static inline void uart_port_set_cons(struct uart_port *up, struct console *con)
up->cons = con;
__uart_port_unlock_irqrestore(up, flags);
}
+
+/* Only for internal port lock wrapper usage. */
+static inline bool __uart_port_using_nbcon(struct uart_port *up)
+{
+ lockdep_assert_held_once(&up->lock);
+
+ if (likely(!uart_console(up)))
+ return false;
+
+ /*
+ * @up->cons is only modified under the port lock. Therefore it is
+ * certain that it cannot disappear here.
+ *
+ * @up->cons->node is added/removed from the console list under the
+ * port lock. Therefore it is certain that the registration status
+ * cannot change here, thus @up->cons->flags can be read directly.
+ */
+ if (hlist_unhashed_lockless(&up->cons->node) ||
+ !(up->cons->flags & CON_NBCON) ||
+ !up->cons->write_atomic) {
+ return false;
+ }
+
+ return true;
+}
+
+/* Only for internal port lock wrapper usage. */
+static inline bool __uart_port_nbcon_try_acquire(struct uart_port *up)
+{
+ if (!__uart_port_using_nbcon(up))
+ return true;
+
+ return nbcon_driver_try_acquire(up->cons);
+}
+
+/* Only for internal port lock wrapper usage. */
+static inline void __uart_port_nbcon_acquire(struct uart_port *up)
+{
+ if (!__uart_port_using_nbcon(up))
+ return;
+
+ while (!nbcon_driver_try_acquire(up->cons))
+ cpu_relax();
+}
+
+/* Only for internal port lock wrapper usage. */
+static inline void __uart_port_nbcon_release(struct uart_port *up)
+{
+ if (!__uart_port_using_nbcon(up))
+ return;
+
+ nbcon_driver_release(up->cons);
+}
+
/**
* uart_port_lock - Lock the UART port
* @up: Pointer to UART port structure
@@ -630,6 +686,7 @@ static inline void uart_port_set_cons(struct uart_port *up, struct console *con)
static inline void uart_port_lock(struct uart_port *up)
{
spin_lock(&up->lock);
+ __uart_port_nbcon_acquire(up);
}

/**
@@ -639,6 +696,7 @@ 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_port_nbcon_acquire(up);
}

/**
@@ -649,6 +707,7 @@ 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_port_nbcon_acquire(up);
}

/**
@@ -659,7 +718,15 @@ 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;
+
+ if (!__uart_port_nbcon_try_acquire(up)) {
+ spin_unlock(&up->lock);
+ return false;
+ }
+
+ return true;
}

/**
@@ -671,7 +738,15 @@ 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;
+
+ if (!__uart_port_nbcon_try_acquire(up)) {
+ spin_unlock_irqrestore(&up->lock, *flags);
+ return false;
+ }
+
+ return true;
}

/**
@@ -680,6 +755,7 @@ static inline bool uart_port_trylock_irqsave(struct uart_port *up, unsigned long
*/
static inline void uart_port_unlock(struct uart_port *up)
{
+ __uart_port_nbcon_release(up);
spin_unlock(&up->lock);
}

@@ -689,6 +765,7 @@ static inline void uart_port_unlock(struct uart_port *up)
*/
static inline void uart_port_unlock_irq(struct uart_port *up)
{
+ __uart_port_nbcon_release(up);
spin_unlock_irq(&up->lock);
}

@@ -699,6 +776,7 @@ 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_port_nbcon_release(up);
spin_unlock_irqrestore(&up->lock, flags);
}

--
2.39.2