Linux Kernels

tty: serial: fsl_lpuart: lock port on console write

This change “tty: serial: fsl_lpuart: lock port on console write” (commit abf1e0a) in Linux kernel is authored by Stefan Agner <stefan [at] agner.ch> on Fri Mar 24 11:33:46 2017 -0700.

Description of "tty: serial: fsl_lpuart: lock port on console write"

The change “tty: serial: fsl_lpuart: lock port on console write” introduces changes as follows.

tty: serial: fsl_lpuart: lock port on console write

The console write code is not entirely race free (e.g. the operations
to disabling the UART interrupts are not atomic) hence locking is
required. This has been become apparent with the PREEMPT RT patchset
applied: With the fully preemptible kernel configuration the system
often ended up in a freeze already at startup.

Disable interrupts and lock using read_lock_irqsave. Try to lock in
the sysrq/oops case, but don't bother if locking fails.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Linux kernel releases containing commit abf1e0a

The Linux kernel releases containing this commit are as follows.

Linux kernel code changes from "tty: serial: fsl_lpuart: lock port on console write"

There are 20 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 drivers/tty/serial/fsl_lpuart.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)
 
diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
index f02934ffb329..15df1ba78095 100644
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -1705,6 +1705,13 @@ lpuart_console_write(struct console *co, const char *s, unsigned int count)
 {
 	struct lpuart_port *sport = lpuart_ports[co->index];
 	unsigned char  old_cr2, cr2;
+	unsigned long flags;
+	int locked = 1;
+
+	if (sport->port.sysrq || oops_in_progress)
+		locked = spin_trylock_irqsave(&sport->port.lock, flags);
+	else
+		spin_lock_irqsave(&sport->port.lock, flags);
 
 	/* first save CR2 and then disable interrupts */
 	cr2 = old_cr2 = readb(sport->port.membase + UARTCR2);
@@ -1719,6 +1726,9 @@ lpuart_console_write(struct console *co, const char *s, unsigned int count)
 		barrier();
 
 	writeb(old_cr2, sport->port.membase + UARTCR2);
+
+	if (locked)
+		spin_unlock_irqrestore(&sport->port.lock, flags);
 }
 
 static void
@@ -1726,6 +1736,13 @@ lpuart32_console_write(struct console *co, const char *s, unsigned int count)
 {
 	struct lpuart_port *sport = lpuart_ports[co->index];
 	unsigned long  old_cr, cr;
+	unsigned long flags;
+	int locked = 1;
+
+	if (sport->port.sysrq || oops_in_progress)
+		locked = spin_trylock_irqsave(&sport->port.lock, flags);
+	else
+		spin_lock_irqsave(&sport->port.lock, flags);
 
 	/* first save CR2 and then disable interrupts */
 	cr = old_cr = lpuart32_read(sport->port.membase + UARTCTRL);
@@ -1740,6 +1757,9 @@ lpuart32_console_write(struct console *co, const char *s, unsigned int count)
 		barrier();
 
 	lpuart32_write(old_cr, sport->port.membase + UARTCTRL);
+
+	if (locked)
+		spin_unlock_irqrestore(&sport->port.lock, flags);
 }
 
 /*

The commit for this change in Linux stable tree is abf1e0a (patch).

Last modified: 2020/01/11 06:40