watchdog: Add support for dynamically allocated watchdog_device structs

If a driver's watchdog_device struct is part of a dynamically allocated
struct (which it often will be), merely locking the module is not enough,
even with a drivers module locked, the driver can be unbound from the device,
examples:
1) The root user can unbind it through sysfd
2) The i2c bus master driver being unloaded for an i2c watchdog

I will gladly admit that these are corner cases, but we still need to handle
them correctly.

The fix for this consists of 2 parts:
1) Add ref / unref operations, so that the driver can refcount the struct
   holding the watchdog_device struct and delay freeing it until any
   open filehandles referring to it are closed
2) Most driver operations will do IO on the device and the driver should not
   do any IO on the device after it has been unbound. Rather then letting each
   driver deal with this internally, it is better to ensure at the watchdog
   core level that no operations (other then unref) will get called after
   the driver has called watchdog_unregister_device(). This actually is the
   bulk of this patch.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

1 files changed, 54 insertions, 1 deletions

diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
index 4d295d2..672d169 100644
--- a/drivers/watchdog/watchdog_dev.c
+++ b/drivers/watchdog/watchdog_dev.c
@@ -65,6 +65,11 @@ static int watchdog_ping(struct watchdog_device *wddev)
 
 	mutex_lock(&wddev->lock);
 
+	if (test_bit(WDOG_UNREGISTERED, &wddev->status)) {
+		err = -ENODEV;
+		goto out_ping;
+	}
+
 	if (!watchdog_active(wddev))
 		goto out_ping;
 
@@ -93,6 +98,11 @@ static int watchdog_start(struct watchdog_device *wddev)
 
 	mutex_lock(&wddev->lock);
 
+	if (test_bit(WDOG_UNREGISTERED, &wddev->status)) {
+		err = -ENODEV;
+		goto out_start;
+	}
+
 	if (watchdog_active(wddev))
 		goto out_start;
 
@@ -121,6 +131,11 @@ static int watchdog_stop(struct watchdog_device *wddev)
 
 	mutex_lock(&wddev->lock);
 
+	if (test_bit(WDOG_UNREGISTERED, &wddev->status)) {
+		err = -ENODEV;
+		goto out_stop;
+	}
+
 	if (!watchdog_active(wddev))
 		goto out_stop;
 
@@ -158,8 +173,14 @@ static int watchdog_get_status(struct watchdog_device *wddev,
 
 	mutex_lock(&wddev->lock);
 
+	if (test_bit(WDOG_UNREGISTERED, &wddev->status)) {
+		err = -ENODEV;
+		goto out_status;
+	}
+
 	*status = wddev->ops->status(wddev);
 
+out_status:
 	mutex_unlock(&wddev->lock);
 	return err;
 }
@@ -185,8 +206,14 @@ static int watchdog_set_timeout(struct watchdog_device *wddev,
 
 	mutex_lock(&wddev->lock);
 
+	if (test_bit(WDOG_UNREGISTERED, &wddev->status)) {
+		err = -ENODEV;
+		goto out_timeout;
+	}
+
 	err = wddev->ops->set_timeout(wddev, timeout);
 
+out_timeout:
 	mutex_unlock(&wddev->lock);
 	return err;
 }
@@ -210,8 +237,14 @@ static int watchdog_get_timeleft(struct watchdog_device *wddev,
 
 	mutex_lock(&wddev->lock);
 
+	if (test_bit(WDOG_UNREGISTERED, &wddev->status)) {
+		err = -ENODEV;
+		goto out_timeleft;
+	}
+
 	*timeleft = wddev->ops->get_timeleft(wddev);
 
+out_timeleft:
 	mutex_unlock(&wddev->lock);
 	return err;
 }
@@ -233,8 +266,14 @@ static int watchdog_ioctl_op(struct watchdog_device *wddev, unsigned int cmd,
 
 	mutex_lock(&wddev->lock);
 
+	if (test_bit(WDOG_UNREGISTERED, &wddev->status)) {
+		err = -ENODEV;
+		goto out_ioctl;
+	}
+
 	err = wddev->ops->ioctl(wddev, cmd, arg);
 
+out_ioctl:
 	mutex_unlock(&wddev->lock);
 	return err;
 }
@@ -398,6 +437,9 @@ static int watchdog_open(struct inode *inode, struct file *file)
 
 	file->private_data = wdd;
 
+	if (wdd->ops->ref)
+		wdd->ops->ref(wdd);
+
 	/* dev/watchdog is a virtual (and thus non-seekable) filesystem */
 	return nonseekable_open(inode, file);
 
@@ -434,7 +476,10 @@ static int watchdog_release(struct inode *inode, struct file *file)
 
 	/* If the watchdog was not stopped, send a keepalive ping */
 	if (err < 0) {
-		dev_crit(wdd->dev, "watchdog did not stop!\n");
+		mutex_lock(&wdd->lock);
+		if (!test_bit(WDOG_UNREGISTERED, &wdd->status))
+			dev_crit(wdd->dev, "watchdog did not stop!\n");
+		mutex_unlock(&wdd->lock);
 		watchdog_ping(wdd);
 	}
 
@@ -444,6 +489,10 @@ static int watchdog_release(struct inode *inode, struct file *file)
 	/* make sure that /dev/watchdog can be re-opened */
 	clear_bit(WDOG_DEV_OPEN, &wdd->status);
 
+	/* Note wdd may be gone after this, do not use after this! */
+	if (wdd->ops->unref)
+		wdd->ops->unref(wdd);
+
 	return 0;
 }
 
@@ -515,6 +564,10 @@ int watchdog_dev_register(struct watchdog_device *watchdog)
 
 int watchdog_dev_unregister(struct watchdog_device *watchdog)
 {
+	mutex_lock(&watchdog->lock);
+	set_bit(WDOG_UNREGISTERED, &watchdog->status);
+	mutex_unlock(&watchdog->lock);
+
 	cdev_del(&watchdog->cdev);
 	if (watchdog->id == 0) {
 		misc_deregister(&watchdog_miscdev);