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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; - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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