[36/65] serial: amba-pl011: lock console writes against interrupts

[Greg KH <gregkh@linuxfoundation.org>]

3.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Rabin Vincent <rabin.vincent@stericsson.com>

commit ef605fdb33883d687cff5ba75095a91b313b4966 upstream.

Protect against pl011_console_write() and the interrupt for
the console UART running concurrently on different CPUs.

Otherwise the console_write could spin for a long time
waiting for the UART to become not busy, while the other
CPU continuously services UART interrupts and keeps the
UART busy.

The checks for sysrq and oops_in_progress are taken
from 8250.c.

Signed-off-by: Rabin Vincent <rabin.vincent@stericsson.com>
Reviewed-by: Srinidhi Kasagar <srinidhi.kasagar@stericsson.com>
Reviewed-by: Bibek Basu <bibek.basu@stericsson.com>
Reviewed-by: Shreshtha Kumar Sahu <shreshthakumar.sahu@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/tty/serial/amba-pl011.c |   14 ++++++++++++++
 1 file changed, 14 insertions(+)

--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -1733,9 +1733,19 @@ pl011_console_write(struct console *co,
 {
 	struct uart_amba_port *uap = amba_ports[co->index];
 	unsigned int status, old_cr, new_cr;
+	unsigned long flags;
+	int locked = 1;
 
 	clk_enable(uap->clk);
 
+	local_irq_save(flags);
+	if (uap->port.sysrq)
+		locked = 0;
+	else if (oops_in_progress)
+		locked = spin_trylock(&uap->port.lock);
+	else
+		spin_lock(&uap->port.lock);
+
 	/*
 	 *	First save the CR then disable the interrupts
 	 */
@@ -1755,6 +1765,10 @@ pl011_console_write(struct console *co,
 	} while (status & UART01x_FR_BUSY);
 	writew(old_cr, uap->port.membase + UART011_CR);
 
+	if (locked)
+		spin_unlock(&uap->port.lock);
+	local_irq_restore(flags);
+
 	clk_disable(uap->clk);
 }