Streamline use of cdevpriv and correct some corner cases.

1) It is not useful to call "devfs_clear_cdevpriv()" from
"d_close" callbacks, hence for example read, write, ioctl and
so on might be sleeping at the time of "d_close" being called
and then then freed private data can still be accessed.
Examples: dtrace, linux_compat, ksyms (all fixed by this patch)

2) In sys/dev/drm* there are some cases in which memory will
be freed twice, if open fails, first by code in the open
routine, secondly by the cdevpriv destructor. Move registration
of the cdevpriv to the end of the drm open routines.

3) devfs_clear_cdevpriv() is not called if the "d_open" callback
registered cdevpriv data and the "d_open" callback function
returned an error. Fix this.

Discussed with:	phk
MFC after:	2 weeks

1 files changed, 6 insertions, 8 deletions

diff --git a/sys/dev/drm2/drm_fops.c b/sys/dev/drm2/drm_fops.c
index 0071783..2685ff7 100644
--- a/sys/dev/drm2/drm_fops.c
+++ b/sys/dev/drm2/drm_fops.c
@@ -57,12 +57,6 @@ int drm_open_helper(struct cdev *kdev, int flags, int fmt, DRM_STRUCTPROC *p,
 		return ENOMEM;
 	}
 
-	retcode = devfs_set_cdevpriv(priv, drm_close);
-	if (retcode != 0) {
-		free(priv, DRM_MEM_FILES);
-		return retcode;
-	}
-
 	DRM_LOCK(dev);
 	priv->dev		= dev;
 	priv->uid		= p->td_ucred->cr_svuid;
@@ -83,7 +77,6 @@ int drm_open_helper(struct cdev *kdev, int flags, int fmt, DRM_STRUCTPROC *p,
 		/* shared code returns -errno */
 		retcode = -dev->driver->open(dev, priv);
 		if (retcode != 0) {
-			devfs_clear_cdevpriv();
 			free(priv, DRM_MEM_FILES);
 			DRM_UNLOCK(dev);
 			return retcode;
@@ -96,7 +89,12 @@ int drm_open_helper(struct cdev *kdev, int flags, int fmt, DRM_STRUCTPROC *p,
 	TAILQ_INSERT_TAIL(&dev->files, priv, link);
 	DRM_UNLOCK(dev);
 	kdev->si_drv1 = dev;
-	return 0;
+
+	retcode = devfs_set_cdevpriv(priv, drm_close);
+	if (retcode != 0)
+		drm_close(priv);
+
+	return (retcode);
 }
 
 static bool