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

[Chris Wilson]

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 at 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