rtc: remove BKL for ioctl()

Remove implicit use of BKL in ioctl() from the RTC framework.

Instead, the rtc->ops_lock is used.  That's the same lock that already
protects the RTC operations when they're issued through the exported
rtc_*() calls in drivers/rtc/interface.c ...  making this a bugfix, not
just a cleanup, since both ioctl calls and set_alarm() need to update IRQ
enable flags and that implies a common lock (which RTC drivers as a rule
do not provide on their own).

A new comment at the declaration of "struct rtc_class_ops" summarizes
current locking rules.  It's not clear to me that the exceptions listed
there should exist ...  if not, those are pre-existing problems which can
be fixed in a patch that doesn't relate to BKL removal.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Jonathan Corbet <corbet@lwn.net>
Acked-by: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/rtc/rtc-dev.c b/drivers/rtc/rtc-dev.c
index 0114a78b7cbbe6687892cca1fad58dc76d8883f9..0a870b7e5c323f5a5411f6c494545d33c023465c 100644 (file)
--- a/drivers/rtc/rtc-dev.c
+++ b/drivers/rtc/rtc-dev.c
@@ -209,7 +209,7 @@ static unsigned int rtc_dev_poll(struct file *file, poll_table *wait)
        return (data != 0) ? (POLLIN | POLLRDNORM) : 0;
 }
 
-static int rtc_dev_ioctl(struct inode *inode, struct file *file,
+static long rtc_dev_ioctl(struct file *file,
                unsigned int cmd, unsigned long arg)
 {
        int err = 0;
@@ -219,6 +219,10 @@ static int rtc_dev_ioctl(struct inode *inode, struct file *file,
        struct rtc_wkalrm alarm;
        void __user *uarg = (void __user *) arg;
 
+       err = mutex_lock_interruptible(&rtc->ops_lock);
+       if (err)
+               return -EBUSY;
+
        /* check that the calling task has appropriate permissions
         * for certain ioctls. doing this check here is useful
         * to avoid duplicate code in each driver.
@@ -227,26 +231,31 @@ static int rtc_dev_ioctl(struct inode *inode, struct file *file,
        case RTC_EPOCH_SET:
        case RTC_SET_TIME:
                if (!capable(CAP_SYS_TIME))
-                       return -EACCES;
+                       err = -EACCES;
                break;
 
        case RTC_IRQP_SET:
                if (arg > rtc->max_user_freq && !capable(CAP_SYS_RESOURCE))
-                       return -EACCES;
+                       err = -EACCES;
                break;
 
        case RTC_PIE_ON:
                if (rtc->irq_freq > rtc->max_user_freq &&
                                !capable(CAP_SYS_RESOURCE))
-                       return -EACCES;
+                       err = -EACCES;
                break;
        }
 
+       if (err)
+               goto done;
+
        /* try the driver's ioctl interface */
        if (ops->ioctl) {
                err = ops->ioctl(rtc->dev.parent, cmd, arg);
-               if (err != -ENOIOCTLCMD)
+               if (err != -ENOIOCTLCMD) {
+                       mutex_unlock(&rtc->ops_lock);
                        return err;
+               }
        }
 
        /* if the driver does not provide the ioctl interface
@@ -265,15 +274,19 @@ static int rtc_dev_ioctl(struct inode *inode, struct file *file,
 
        switch (cmd) {
        case RTC_ALM_READ:
+               mutex_unlock(&rtc->ops_lock);
+
                err = rtc_read_alarm(rtc, &alarm);
                if (err < 0)
                        return err;
 
                if (copy_to_user(uarg, &alarm.time, sizeof(tm)))
-                       return -EFAULT;
-               break;
+                       err = -EFAULT;
+               return err;
 
        case RTC_ALM_SET:
+               mutex_unlock(&rtc->ops_lock);
+
                if (copy_from_user(&alarm.time, uarg, sizeof(tm)))
                        return -EFAULT;
 
@@ -321,24 +334,26 @@ static int rtc_dev_ioctl(struct inode *inode, struct file *file,
                        }
                }
 
-               err = rtc_set_alarm(rtc, &alarm);
-               break;
+               return rtc_set_alarm(rtc, &alarm);
 
        case RTC_RD_TIME:
+               mutex_unlock(&rtc->ops_lock);
+
                err = rtc_read_time(rtc, &tm);
                if (err < 0)
                        return err;
 
                if (copy_to_user(uarg, &tm, sizeof(tm)))
-                       return -EFAULT;
-               break;
+                       err = -EFAULT;
+               return err;
 
        case RTC_SET_TIME:
+               mutex_unlock(&rtc->ops_lock);
+
                if (copy_from_user(&tm, uarg, sizeof(tm)))
                        return -EFAULT;
 
-               err = rtc_set_time(rtc, &tm);
-               break;
+               return rtc_set_time(rtc, &tm);
 
        case RTC_PIE_ON:
                err = rtc_irq_set_state(rtc, NULL, 1);
@@ -376,34 +391,37 @@ static int rtc_dev_ioctl(struct inode *inode, struct file *file,
                break;
 #endif
        case RTC_WKALM_SET:
+               mutex_unlock(&rtc->ops_lock);
                if (copy_from_user(&alarm, uarg, sizeof(alarm)))
                        return -EFAULT;
 
-               err = rtc_set_alarm(rtc, &alarm);
-               break;
+               return rtc_set_alarm(rtc, &alarm);
 
        case RTC_WKALM_RD:
+               mutex_unlock(&rtc->ops_lock);
                err = rtc_read_alarm(rtc, &alarm);
                if (err < 0)
                        return err;
 
                if (copy_to_user(uarg, &alarm, sizeof(alarm)))
-                       return -EFAULT;
-               break;
+                       err = -EFAULT;
+               return err;
 
 #ifdef CONFIG_RTC_INTF_DEV_UIE_EMUL
        case RTC_UIE_OFF:
                clear_uie(rtc);
-               return 0;
+               break;
 
        case RTC_UIE_ON:
-               return set_uie(rtc);
+               err = set_uie(rtc);
 #endif
        default:
                err = -ENOTTY;
                break;
        }
 
+done:
+       mutex_unlock(&rtc->ops_lock);
        return err;
 }
 
@@ -432,7 +450,7 @@ static const struct file_operations rtc_dev_fops = {
        .llseek         = no_llseek,
        .read           = rtc_dev_read,
        .poll           = rtc_dev_poll,
-       .ioctl          = rtc_dev_ioctl,
+       .unlocked_ioctl = rtc_dev_ioctl,
        .open           = rtc_dev_open,
        .release        = rtc_dev_release,
        .fasync         = rtc_dev_fasync,

diff --git a/include/linux/rtc.h b/include/linux/rtc.h
index f2d0d15277216f9655ab254f3f9c9ef3ea471972..b01fe004cb5e5787ebc8e08ca514918a9b782fa6 100644 (file)
--- a/include/linux/rtc.h
+++ b/include/linux/rtc.h
@@ -115,6 +115,23 @@ extern void rtc_time_to_tm(unsigned long time, struct rtc_time *tm);
 
 extern struct class *rtc_class;
 
+/*
+ * For these RTC methods the device parameter is the physical device
+ * on whatever bus holds the hardware (I2C, Platform, SPI, etc), which
+ * was passed to rtc_device_register().  Its driver_data normally holds
+ * device state, including the rtc_device pointer for the RTC.
+ *
+ * Most of these methods are called with rtc_device.ops_lock held,
+ * through the rtc_*(struct rtc_device *, ...) calls.
+ *
+ * The (current) exceptions are mostly filesystem hooks:
+ *   - the proc() hook for procfs
+ *   - non-ioctl() chardev hooks:  open(), release(), read_callback()
+ *   - periodic irq calls:  irq_set_state(), irq_set_freq()
+ *
+ * REVISIT those periodic irq calls *do* have ops_lock when they're
+ * issued through ioctl() ...
+ */
 struct rtc_class_ops {
        int (*open)(struct device *);
        void (*release)(struct device *);