[PATCH] drm: Restore drm_file->is_master

[Chris Wilson]

Despite the claims of

commit 48ba813701eb14b3008edefef4a0789b328e278c
Author: David Herrmann <dh.herrmann at gmail.com>
Date:   Tue Jul 22 18:46:09 2014 +0200

    drm: drop redundant drm_file->is_master

drm_file->is_master is not synomous with having drm_file->master ==
drm_file->minor->master. This is because drm_file->master is the same
for all drm_files of the same generation and so when there is a master,
every drm_file believes itself to be the master. Confusion ensues and
things go pear shaped when one file is closed and there is no master
anymore.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=82283
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Alex Deucher <alexander.deucher at amd.com>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: David Herrmann <dh.herrmann at gmail.com>
---
 drivers/gpu/drm/drm_drv.c  |  5 ++---
 drivers/gpu/drm/drm_fops.c | 12 ++++++------
 include/drm/drmP.h         |  3 ++-
 3 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index a1863d8..76cdb51 100644
--- a/drivers/gpu/drm/drm_drv.c
+++ b/drivers/gpu/drm/drm_drv.c
@@ -198,6 +198,7 @@ int drm_setmaster_ioctl(struct drm_device *dev, void *data,
 		if (unlikely(ret != 0))
 			drm_master_put(&file_priv->minor->master);
 	}
+	file_priv->is_master = ret == 0;
 
 out_unlock:
 	mutex_unlock(&dev->master_mutex);
@@ -213,13 +214,11 @@ int drm_dropmaster_ioctl(struct drm_device *dev, void *data,
 	if (!drm_is_master(file_priv))
 		goto out_unlock;
 
-	if (!file_priv->minor->master)
-		goto out_unlock;
-
 	ret = 0;
 	if (dev->driver->master_drop)
 		dev->driver->master_drop(dev, file_priv, false);
 	drm_master_put(&file_priv->minor->master);
+	file_priv->is_master = false;
 
 out_unlock:
 	mutex_unlock(&dev->master_mutex);
diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c
index c0166ba..083f7b9 100644
--- a/drivers/gpu/drm/drm_fops.c
+++ b/drivers/gpu/drm/drm_fops.c
@@ -196,6 +196,7 @@ static int drm_open_helper(struct file *filp, struct drm_minor *minor)
 
 		/* take another reference for the copy in the local file priv */
 		priv->master = drm_master_get(priv->minor->master);
+		priv->is_master = true;
 		priv->authenticated = 1;
 
 		if (dev->driver->master_create) {
@@ -434,12 +435,11 @@ int drm_release(struct inode *inode, struct file *filp)
 		}
 		mutex_unlock(&dev->struct_mutex);
 
-		if (file_priv->minor->master == file_priv->master) {
-			/* drop the reference held my the minor */
-			if (dev->driver->master_drop)
-				dev->driver->master_drop(dev, file_priv, true);
-			drm_master_put(&file_priv->minor->master);
-		}
+		/* drop the reference held my the minor */
+		if (dev->driver->master_drop)
+			dev->driver->master_drop(dev, file_priv, true);
+		drm_master_put(&file_priv->minor->master);
+		file_priv->is_master = false;
 	}
 
 	/* drop the master reference held by the file priv */
diff --git a/include/drm/drmP.h b/include/drm/drmP.h
index 0ffce5c..70a6598 100644
--- a/include/drm/drmP.h
+++ b/include/drm/drmP.h
@@ -378,6 +378,7 @@ struct drm_prime_file_private {
 
 /** File private data */
 struct drm_file {
+	bool is_master:1;
 	unsigned authenticated :1;
 	/* true when the client has asked us to expose stereo 3D mode flags */
 	unsigned stereo_allowed :1;
@@ -1177,7 +1178,7 @@ static inline bool drm_is_primary_client(const struct drm_file *file_priv)
  */
 static inline bool drm_is_master(const struct drm_file *file)
 {
-	return file->master && file->master == file->minor->master;
+	return file->is_master;
 }
 
 /******************************************************************/
-- 
1.9.1