linux-kernel - [51/89] serial: amba-pl011: lock console writes against interrupts

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Message-Id: <20120201210048.391552990@clark.kroah.org>
Date:	Wed, 01 Feb 2012 13:00:15 -0800
From:	Greg KH <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk,
	Rabin Vincent <rabin.vincent@...ricsson.com>,
	Srinidhi Kasagar <srinidhi.kasagar@...ricsson.com>,
	Bibek Basu <bibek.basu@...ricsson.com>,
	Shreshtha Kumar Sahu <shreshthakumar.sahu@...ricsson.com>,
	Linus Walleij <linus.walleij@...aro.org>
Subject: [51/89] serial: amba-pl011: lock console writes against interrupts

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

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

From: Rabin Vincent <rabin.vincent@...ricsson.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@...ricsson.com>
Reviewed-by: Srinidhi Kasagar <srinidhi.kasagar@...ricsson.com>
Reviewed-by: Bibek Basu <bibek.basu@...ricsson.com>
Reviewed-by: Shreshtha Kumar Sahu <shreshthakumar.sahu@...ricsson.com>
Signed-off-by: Linus Walleij <linus.walleij@...aro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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
@@ -1740,9 +1740,19 @@ 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
 	 */
@@ -1762,6 +1772,10 @@ 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);
 }
 


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