linux-kernel - [PATCH RFC] PPC-BRIQ_PANEL: Remove BKL and replace with atomic variable.

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Date:	Sun, 18 Oct 2009 21:39:22 +0200 (CEST)
From:	John Kacur <jkacur@...hat.com>
To:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Arnd Bergmann <arndbergmann@...glemail.com>,
	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: [PATCH RFC] PPC-BRIQ_PANEL: Remove BKL and replace with atomic
 variable.

>From b64c7d0f11eab96cb253b23c7264c999746116c0 Mon Sep 17 00:00:00 2001
From: John Kacur <jkacur@...hat.com>
Date: Sun, 18 Oct 2009 21:29:21 +0200
Subject: [PATCH] PPC-BRIQ_PANEL: Remove BKL and replace with atomic variable.

There are no locks here except the bkl in briq_panel_open. It's only
purpose is to ensure single access. Remove the bkl and ensure single access
by making vfd_is_open an atomic_variable.

Signed-off-by: John Kacur <jkacur@...hat.com>
---
 drivers/char/briq_panel.c |   25 ++++++++-----------------
 1 files changed, 8 insertions(+), 17 deletions(-)

diff --git a/drivers/char/briq_panel.c b/drivers/char/briq_panel.c
index d8cff90..5396df4 100644
--- a/drivers/char/briq_panel.c
+++ b/drivers/char/briq_panel.c
@@ -6,7 +6,6 @@
 
 #include <linux/module.h>
 
-#include <linux/smp_lock.h>
 #include <linux/types.h>
 #include <linux/errno.h>
 #include <linux/tty.h>
@@ -25,6 +24,7 @@
 #include <asm/uaccess.h>
 #include <asm/io.h>
 #include <asm/prom.h>
+#include <asm/atomic.h>
 
 #define		BRIQ_PANEL_MINOR	156
 #define		BRIQ_PANEL_VFD_IOPORT	0x0390
@@ -32,7 +32,7 @@
 #define		BRIQ_PANEL_VER		"1.1 (04/20/2002)"
 #define		BRIQ_PANEL_MSG0		"Loading Linux"
 
-static int		vfd_is_open;
+static atomic_t vfd_is_open = ATOMIC_INIT(0);
 static unsigned char	vfd[40];
 static int		vfd_cursor;
 static unsigned char	ledpb, led;
@@ -68,35 +68,26 @@ static void set_led(char state)
 
 static int briq_panel_open(struct inode *ino, struct file *filep)
 {
-	lock_kernel();
-	/* enforce single access, vfd_is_open is protected by BKL */
-	if (vfd_is_open) {
-		unlock_kernel();
+	/* enforce single access */
+	if (atomic_cmpxchg(vfd_is_open, 0, 1))
 		return -EBUSY;
-	}
-	vfd_is_open = 1;
-
-	unlock_kernel();
 	return 0;
 }
 
 static int briq_panel_release(struct inode *ino, struct file *filep)
 {
-	if (!vfd_is_open)
+	if (!atomic_cmpxchg(vfd_is_open, 1, 0))
 		return -ENODEV;
-
-	vfd_is_open = 0;
-
 	return 0;
 }
 
-static ssize_t briq_panel_read(struct file *file, char __user *buf, size_t count,
-			 loff_t *ppos)
+static ssize_t briq_panel_read(struct file *file, char __user *buf,
+		size_t count, loff_t *ppos)
 {
 	unsigned short c;
 	unsigned char cp;
 
-	if (!vfd_is_open)
+	if (!atomic_read(vfd_is_open))
 		return -ENODEV;
 
 	c = (inb(BRIQ_PANEL_LED_IOPORT) & 0x000c) | (ledpb & 0x0003);
-- 
1.6.0.6

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