2007-12-02 22:00:35

by Jiri Kosina

Subject: [RESEND] [PATCH] RTC: assure proper memory ordering with respect to RTC_DEV_BUSY flag (was Re: RTC: convert mutex to bitfield)

[ nobody seems to have picked this up, resending. This is a fix for
commit 8853c202b4 in Linus' tree ]

From: Jiri Kosina <[email protected]>

RTC: assure proper memory ordering with respect to RTC_DEV_BUSY flag

We must make sure that the RTC_DEV_BUSY flag has proper lock semantics,
i.e. that the RTC_DEV_BUSY stores clearing the flag don't get reordered
before the preceeding stores and loads and vice versa.

Spotted by Nick Piggin.

Signed-off-by: Jiri Kosina <[email protected]>

diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c
index a4f56e9..f1e00ff 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 (test_and_set_bit(RTC_DEV_BUSY, &rtc->flags))
+ if (test_and_set_bit_lock(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);

- clear_bit(RTC_DEV_BUSY, &rtc->flags);
+ clear_bit_unlock(RTC_DEV_BUSY, &rtc->flags);

return retval;
}
diff --git a/drivers/rtc/rtc-dev.c b/drivers/rtc/rtc-dev.c
index ae1bf17..025c60a 100644
--- a/drivers/rtc/rtc-dev.c
+++ b/drivers/rtc/rtc-dev.c
@@ -26,7 +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;

- if (test_and_set_bit(RTC_DEV_BUSY, &rtc->flags))
+ if (test_and_set_bit_lock(RTC_DEV_BUSY, &rtc->flags))
return -EBUSY;

file->private_data = rtc;
@@ -41,7 +41,7 @@ static int rtc_dev_open(struct inode *inode, struct file *file)
}

/* something has gone wrong */
- clear_bit(RTC_DEV_BUSY, &rtc->flags);
+ clear_bit_unlock(RTC_DEV_BUSY, &rtc->flags);
return err;
}

@@ -402,7 +402,7 @@ static int rtc_dev_release(struct inode *inode, struct file *file)
if (rtc->ops->release)
rtc->ops->release(rtc->dev.parent);

- clear_bit(RTC_DEV_BUSY, &rtc->flags);
+ clear_bit_unlock(RTC_DEV_BUSY, &rtc->flags);
return 0;
}

2007-12-02 22:16:27

by Alessandro Zummo

Subject: Re: [RESEND] [PATCH] RTC: assure proper memory ordering with respect to RTC_DEV_BUSY flag (was Re: RTC: convert mutex to bitfield)

On Sun, 2 Dec 2007 23:00:04 +0100 (CET)
Jiri Kosina <[email protected]> wrote:

> [ nobody seems to have picked this up, resending. This is a fix for
> commit 8853c202b4 in Linus' tree ]
>
> From: Jiri Kosina <[email protected]>
>
> RTC: assure proper memory ordering with respect to RTC_DEV_BUSY flag
>
> We must make sure that the RTC_DEV_BUSY flag has proper lock semantics,
> i.e. that the RTC_DEV_BUSY stores clearing the flag don't get reordered
> before the preceeding stores and loads and vice versa.
>
> Spotted by Nick Piggin.
>
> Signed-off-by: Jiri Kosina <[email protected]>

missed it, sorry.


Acked-by: Alessandro Zummo <[email protected]>

--

Best regards,

Alessandro Zummo,
Tower Technologies - Torino, Italy

http://www.towertech.it