diff --git a/drivers/char/snsc.c b/drivers/char/snsc.c
index 8fe099a41065..0b799ac1b049 100644
--- a/drivers/char/snsc.c
+++ b/drivers/char/snsc.c
@@ -21,6 +21,7 @@
 #include <linux/poll.h>
 #include <linux/module.h>
 #include <linux/slab.h>
+#include <linux/smp_lock.h>
 #include <asm/sn/io.h>
 #include <asm/sn/sn_sal.h>
 #include <asm/sn/module.h>
@@ -104,6 +105,7 @@ scdrv_open(struct inode *inode, struct file *file)
 	file->private_data = sd;
 
 	/* hook this subchannel up to the system controller interrupt */
+	lock_kernel();
 	rv = request_irq(SGI_UART_VECTOR, scdrv_interrupt,
 			 IRQF_SHARED | IRQF_DISABLED,
 			 SYSCTL_BASENAME, sd);
@@ -111,9 +113,10 @@ scdrv_open(struct inode *inode, struct file *file)
 		ia64_sn_irtr_close(sd->sd_nasid, sd->sd_subch);
 		kfree(sd);
 		printk("%s: irq request failed (%d)\n", __func__, rv);
+		unlock_kernel();
 		return -EBUSY;
 	}
-
+	unlock_kernel();
 	return 0;
 }