[PATCH] drm: Use global_mutex to serialise open/lastclose

[Chris Wilson <chris@chris-wilson.co.uk>]

Dave Airlie:
  I might be missing something, but what stops the race with something
  reopening while we are in lastclose now?

The global_mutex which appears to fill this role is only taken inside
the drm_stub_open() and not drm_open() itself. As that mutex appears to
serve no other role, retask it to serialise open/lastclose.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/drm_fops.c |   35 ++++++++++++++++++-----------------
 1 files changed, 18 insertions(+), 17 deletions(-)

diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c
index 6367961..71bcd1b 100644
--- a/drivers/gpu/drm/drm_fops.c
+++ b/drivers/gpu/drm/drm_fops.c
@@ -123,27 +123,30 @@ int drm_open(struct inode *inode, struct file *filp)
 	struct drm_device *dev = NULL;
 	int minor_id = iminor(inode);
 	struct drm_minor *minor;
-	int retcode = 0;
+	int retcode = -ENODEV;
 
+	mutex_lock(&drm_global_mutex);
 	minor = idr_find(&drm_minors_idr, minor_id);
 	if (!minor)
-		return -ENODEV;
+		goto err;
 
 	if (!(dev = minor->dev))
-		return -ENODEV;
+		goto err;
 
 	retcode = drm_open_helper(inode, filp, dev);
-	if (!retcode) {
-		atomic_inc(&dev->counts[_DRM_STAT_OPENS]);
-		spin_lock(&dev->count_lock);
-		if (!dev->open_count++) {
-			spin_unlock(&dev->count_lock);
-			retcode = drm_setup(dev);
-			goto out;
-		}
+	if (retcode)
+		goto err;
+
+	atomic_inc(&dev->counts[_DRM_STAT_OPENS]);
+	spin_lock(&dev->count_lock);
+	if (!dev->open_count++) {
 		spin_unlock(&dev->count_lock);
-	}
-out:
+		retcode = drm_setup(dev);
+	} else
+		spin_unlock(&dev->count_lock);
+err:
+	mutex_unlock(&drm_global_mutex);
+
 	if (!retcode) {
 		mutex_lock(&dev->struct_mutex);
 		if (minor->type == DRM_MINOR_LEGACY) {
@@ -178,7 +181,6 @@ int drm_stub_open(struct inode *inode, struct file *filp)
 
 	DRM_DEBUG("\n");
 
-	mutex_lock(&drm_global_mutex);
 	minor = idr_find(&drm_minors_idr, minor_id);
 	if (!minor)
 		goto out;
@@ -198,8 +200,8 @@ int drm_stub_open(struct inode *inode, struct file *filp)
 	}
 	fops_put(old_fops);
 
+	ret = 0;
 out:
-	mutex_unlock(&drm_global_mutex);
 	return err;
 }
 
@@ -474,8 +476,6 @@ int drm_release(struct inode *inode, struct file *filp)
 	struct drm_device *dev = file_priv->minor->dev;
 	int retcode = 0;
 
-	mutex_lock(&drm_global_mutex);
-
 	DRM_DEBUG("open_count = %d\n", dev->open_count);
 
 	if (dev->driver->preclose)
@@ -569,6 +569,7 @@ int drm_release(struct inode *inode, struct file *filp)
 	 * End inline drm_release
 	 */
 
+	mutex_lock(&drm_global_mutex);
 	atomic_inc(&dev->counts[_DRM_STAT_CLOSES]);
 	spin_lock(&dev->count_lock);
 	if (!--dev->open_count) {
-- 
1.7.1