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Message-ID: <Pine.LNX.4.64.0710281211170.18815@twin.jikos.cz>
Date: Sun, 28 Oct 2007 12:12:19 +0100 (CET)
From: Jiri Kosina <jikos@...os.cz>
To: Andrew Morton <akpm@...ux-foundation.org>
cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Gabriel C <nix.or.die@...glemail.com>, a.zummo@...ertech.it,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
rtc-linux@...glegroups.com
Subject: Re: BUG: lock held when returning to user space
(CC list stripped)
On Sat, 27 Oct 2007, Andrew Morton wrote:
> It's a fairly daft thing to do. I think it'd be saner to teach rtc about
> test_and_set_bit() personally..
From: Jiri Kosina <jkosina@...e.cz>
RTC: convert mutex to bitfield
RTC code is using mutex to assure exclusive access to /dev/rtc.
This is however wrong usage, as it leaves the mutex locked when
returning into userspace, which is unacceptable.
Convert rtc->char_lock into bit operation.
Signed-off-by: Jiri Kosina <jkosina@...e.cz>
diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c
index de0da54..a4f56e9 100644
--- a/drivers/rtc/interface.c
+++ b/drivers/rtc/interface.c
@@ -293,7 +293,7 @@ int rtc_irq_register(struct rtc_device *rtc, struct rtc_task *task)
return -EINVAL;
/* Cannot register while the char dev is in use */
- if (!(mutex_trylock(&rtc->char_lock)))
+ if (test_and_set_bit(RTC_DEV_BUSY, &rtc->flags))
return -EBUSY;
spin_lock_irq(&rtc->irq_task_lock);
@@ -303,7 +303,7 @@ int rtc_irq_register(struct rtc_device *rtc, struct rtc_task *task)
}
spin_unlock_irq(&rtc->irq_task_lock);
- mutex_unlock(&rtc->char_lock);
+ clear_bit(RTC_DEV_BUSY, &rtc->flags);
return retval;
}
diff --git a/drivers/rtc/rtc-dev.c b/drivers/rtc/rtc-dev.c
index 814583b..ae1bf17 100644
--- a/drivers/rtc/rtc-dev.c
+++ b/drivers/rtc/rtc-dev.c
@@ -26,10 +26,7 @@ static int rtc_dev_open(struct inode *inode, struct file *file)
struct rtc_device, char_dev);
const struct rtc_class_ops *ops = rtc->ops;
- /* We keep the lock as long as the device is in use
- * and return immediately if busy
- */
- if (!(mutex_trylock(&rtc->char_lock)))
+ if (test_and_set_bit(RTC_DEV_BUSY, &rtc->flags))
return -EBUSY;
file->private_data = rtc;
@@ -43,8 +40,8 @@ static int rtc_dev_open(struct inode *inode, struct file *file)
return 0;
}
- /* something has gone wrong, release the lock */
- mutex_unlock(&rtc->char_lock);
+ /* something has gone wrong */
+ clear_bit(RTC_DEV_BUSY, &rtc->flags);
return err;
}
@@ -405,7 +402,7 @@ static int rtc_dev_release(struct inode *inode, struct file *file)
if (rtc->ops->release)
rtc->ops->release(rtc->dev.parent);
- mutex_unlock(&rtc->char_lock);
+ clear_bit(RTC_DEV_BUSY, &rtc->flags);
return 0;
}
@@ -440,7 +437,6 @@ void rtc_dev_prepare(struct rtc_device *rtc)
rtc->dev.devt = MKDEV(MAJOR(rtc_devt), rtc->id);
- mutex_init(&rtc->char_lock);
#ifdef CONFIG_RTC_INTF_DEV_UIE_EMUL
INIT_WORK(&rtc->uie_task, rtc_uie_task);
setup_timer(&rtc->uie_timer, rtc_uie_timer, (unsigned long)rtc);
diff --git a/include/linux/rtc.h b/include/linux/rtc.h
index 6d5e4a4..f2d0d15 100644
--- a/include/linux/rtc.h
+++ b/include/linux/rtc.h
@@ -133,6 +133,9 @@ struct rtc_class_ops {
#define RTC_DEVICE_NAME_SIZE 20
struct rtc_task;
+/* flags */
+#define RTC_DEV_BUSY 0
+
struct rtc_device
{
struct device dev;
@@ -145,7 +148,7 @@ struct rtc_device
struct mutex ops_lock;
struct cdev char_dev;
- struct mutex char_lock;
+ unsigned long flags;
unsigned long irq_data;
spinlock_t irq_lock;
-
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