From: Andrew Morton <akpm@osdl.org>
Date: Fri, 30 Jun 2006 09:29:59 +0000 (-0700)
Subject: [SERIAL] 8250: sysrq deadlock fix
X-Git-Tag: v2.6.18-rc2~84^2
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=68aa2c0d4a36b43ea9c6d77134c94b4501fd2eb4;p=linux-2.6

[SERIAL] 8250: sysrq deadlock fix

Fix http://bugzilla.kernel.org/show_bug.cgi?id=6716

Doing a sysrq over a serial line into an SMP machine presently deadlocks.

Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
---

diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c
index 5443fcd383..0ae9ced00e 100644
--- a/drivers/serial/8250.c
+++ b/drivers/serial/8250.c
@@ -2252,10 +2252,14 @@ serial8250_console_write(struct console *co, const char *s, unsigned int count)
 
 	touch_nmi_watchdog();
 
-	if (oops_in_progress) {
-		locked = spin_trylock_irqsave(&up->port.lock, flags);
+	local_irq_save(flags);
+	if (up->port.sysrq) {
+		/* serial8250_handle_port() already took the lock */
+		locked = 0;
+	} else if (oops_in_progress) {
+		locked = spin_trylock(&up->port.lock);
 	} else
-		spin_lock_irqsave(&up->port.lock, flags);
+		spin_lock(&up->port.lock);
 
 	/*
 	 *	First save the IER then disable the interrupts
@@ -2277,7 +2281,8 @@ serial8250_console_write(struct console *co, const char *s, unsigned int count)
 	serial_out(up, UART_IER, ier);
 
 	if (locked)
-		spin_unlock_irqrestore(&up->port.lock, flags);
+		spin_unlock(&up->port.lock);
+	local_irq_restore(flags);
 }
 
 static int serial8250_console_setup(struct console *co, char *options)