From bad75cb0ebe9409409f68f9fd21a8434d43bc258 Mon Sep 17 00:00:00 2001
From: mb <mb@3c298f89-4303-0410-b956-a3cf2f4a3e73>
Date: Wed, 19 Mar 2008 11:32:08 +0000
Subject: [PATCH] GPIODEV: Fix open-count race condition.
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@10625 3c298f89-4303-0410-b956-a3cf2f4a3e73
---
.../generic-2.6/files/drivers/gpio/gpio_dev.c | 21 ++++++++++++-------
1 file changed, 14 insertions(+), 7 deletions(-)
diff --git a/target/linux/generic-2.6/files/drivers/gpio/gpio_dev.c b/target/linux/generic-2.6/files/drivers/gpio/gpio_dev.c
index 690a3fb8c..48ef76f8a 100644
--- a/target/linux/generic-2.6/files/drivers/gpio/gpio_dev.c
+++ b/target/linux/generic-2.6/files/drivers/gpio/gpio_dev.c
@@ -25,6 +25,7 @@
#include <asm/uaccess.h>
#include <asm/io.h>
#include <asm/gpio.h>
+#include <asm/atomic.h>
#include <linux/init.h>
#include <linux/genhd.h>
#include <linux/device.h>
@@ -35,10 +36,12 @@
#define DEVNAME "gpio"
static int dev_major;
-static int gpio_is_open = 0;
-unsigned int gpio_access_mask = 0;
+static unsigned int gpio_access_mask;
static struct class *gpio_class;
+/* Counter is 1, if the device is not opened and zero (or less) if opened. */
+static atomic_t gpio_open_cnt = ATOMIC_INIT(1);
+
static int
gpio_ioctl(struct inode * inode, struct file * file, unsigned int cmd, unsigned long arg)
{
@@ -94,15 +97,18 @@ gpio_open(struct inode *inode, struct file *file)
goto out;
}
- if (gpio_is_open)
- {
+ /* FIXME: We should really allow multiple applications to open the device
+ * at the same time, as long as the apps access different IO pins.
+ * The generic gpio-registration functions can be used for that.
+ * Two new IOCTLs have to be introduced for that. Need to check userspace
+ * compatibility first. --mb */
+ if (!atomic_dec_and_test(&gpio_open_cnt)) {
+ atomic_inc(&gpio_open_cnt);
printk(KERN_ERR DRVNAME ": Device with minor ID %d already in use\n", dev_minor);
result = -EBUSY;
goto out;
}
- gpio_is_open = 1;
-
out:
return result;
}
@@ -110,7 +116,8 @@ out:
static int
gpio_close(struct inode * inode, struct file * file)
{
- gpio_is_open = 0;
+ smp_mb__before_atomic_inc();
+ atomic_inc(&gpio_open_cnt);
return 0;
}
--
2.20.1