drm: make minors independent of global lock

We used to protect minor-lookup and setup by the global drm lock. To
continue our attempts of dropping drm_global_mutex, this patch makes the
minor management independent of it. Furthermore, we make it all atomic and
switch to spin-locks instead of a mutex.

Now that minor-lookup is independent, we also move the
"drm_is_unplugged()" test into the minor-lookup path. There is no reason
to ever return a minor for unplugged objects, so keep that logic internal.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>

diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c
index 4ce5318d14bc782812ce1d43486e902194b8f92b..8f46fe273ba30be8d778f38bf8ce4b7699e44a8c 100644 (file)
--- a/drivers/gpu/drm/drm_fops.c
+++ b/drivers/gpu/drm/drm_fops.c
@@ -39,7 +39,7 @@
 #include <linux/slab.h>
 #include <linux/module.h>
 
-/* from BKL pushdown: note that nothing else serializes idr_find() */
+/* from BKL pushdown */
 DEFINE_MUTEX(drm_global_mutex);
 EXPORT_SYMBOL(drm_global_mutex);
 
@@ -91,11 +91,6 @@ int drm_open(struct inode *inode, struct file *filp)
                return PTR_ERR(minor);
 
        dev = minor->dev;
-       if (drm_device_is_unplugged(dev)) {
-               retcode = -ENODEV;
-               goto err_release;
-       }
-
        if (!dev->open_count++)
                need_setup = 1;
        mutex_lock(&dev->struct_mutex);
@@ -127,7 +122,6 @@ err_undo:
        dev->dev_mapping = old_mapping;
        mutex_unlock(&dev->struct_mutex);
        dev->open_count--;
-err_release:
        drm_minor_release(minor);
        return retcode;
 }
@@ -157,9 +151,6 @@ int drm_stub_open(struct inode *inode, struct file *filp)
                goto out_unlock;
 
        dev = minor->dev;
-       if (drm_device_is_unplugged(dev))
-               goto out_release;
-
        new_fops = fops_get(dev->driver->fops);
        if (!new_fops)
                goto out_release;

diff --git a/drivers/gpu/drm/drm_stub.c b/drivers/gpu/drm/drm_stub.c
index 83ef4a63358cf1227325a06ab90d57f13642a209..c23eaf6442ff95b15c02164805e18de8769fdbdb 100644 (file)
--- a/drivers/gpu/drm/drm_stub.c
+++ b/drivers/gpu/drm/drm_stub.c
@@ -70,6 +70,7 @@ module_param_named(vblankoffdelay, drm_vblank_offdelay, int, 0600);
 module_param_named(timestamp_precision_usec, drm_timestamp_precision, int, 0600);
 module_param_named(timestamp_monotonic, drm_timestamp_monotonic, int, 0600);
 
+static DEFINE_SPINLOCK(drm_minor_lock);
 struct idr drm_minors_idr;
 
 struct class *drm_class;
@@ -240,6 +241,19 @@ int drm_dropmaster_ioctl(struct drm_device *dev, void *data,
        return 0;
 }
 
+/*
+ * DRM Minors
+ * A DRM device can provide several char-dev interfaces on the DRM-Major. Each
+ * of them is represented by a drm_minor object. Depending on the capabilities
+ * of the device-driver, different interfaces are registered.
+ *
+ * Minors can be accessed via dev->$minor_name. This pointer is either
+ * NULL or a valid drm_minor pointer and stays valid as long as the device is
+ * valid. This means, DRM minors have the same life-time as the underlying
+ * device. However, this doesn't mean that the minor is active. Minors are
+ * registered and unregistered dynamically according to device-state.
+ */
+
 static struct drm_minor **drm_minor_get_slot(struct drm_device *dev,
                                             unsigned int type)
 {
@@ -285,6 +299,7 @@ static void drm_minor_free(struct drm_device *dev, unsigned int type)
 static int drm_minor_register(struct drm_device *dev, unsigned int type)
 {
        struct drm_minor *new_minor;
+       unsigned long flags;
        int ret;
        int minor_id;
 
@@ -294,19 +309,21 @@ static int drm_minor_register(struct drm_device *dev, unsigned int type)
        if (!new_minor)
                return 0;
 
+       idr_preload(GFP_KERNEL);
+       spin_lock_irqsave(&drm_minor_lock, flags);
        minor_id = idr_alloc(&drm_minors_idr,
                             NULL,
                             64 * type,
                             64 * (type + 1),
-                            GFP_KERNEL);
+                            GFP_NOWAIT);
+       spin_unlock_irqrestore(&drm_minor_lock, flags);
+       idr_preload_end();
 
        if (minor_id < 0)
                return minor_id;
 
        new_minor->index = minor_id;
 
-       idr_replace(&drm_minors_idr, new_minor, minor_id);
-
        ret = drm_debugfs_init(new_minor, minor_id, drm_debugfs_root);
        if (ret) {
                DRM_ERROR("DRM: Failed to initialize /sys/kernel/debug/dri.\n");
@@ -319,27 +336,40 @@ static int drm_minor_register(struct drm_device *dev, unsigned int type)
                goto err_debugfs;
        }
 
+       /* replace NULL with @minor so lookups will succeed from now on */
+       spin_lock_irqsave(&drm_minor_lock, flags);
+       idr_replace(&drm_minors_idr, new_minor, new_minor->index);
+       spin_unlock_irqrestore(&drm_minor_lock, flags);
+
        DRM_DEBUG("new minor assigned %d\n", minor_id);
        return 0;
 
 err_debugfs:
        drm_debugfs_cleanup(new_minor);
 err_id:
+       spin_lock_irqsave(&drm_minor_lock, flags);
        idr_remove(&drm_minors_idr, minor_id);
+       spin_unlock_irqrestore(&drm_minor_lock, flags);
+       new_minor->index = 0;
        return ret;
 }
 
 static void drm_minor_unregister(struct drm_device *dev, unsigned int type)
 {
        struct drm_minor *minor;
+       unsigned long flags;
 
        minor = *drm_minor_get_slot(dev, type);
        if (!minor || !minor->kdev)
                return;
 
+       spin_lock_irqsave(&drm_minor_lock, flags);
+       idr_remove(&drm_minors_idr, minor->index);
+       spin_unlock_irqrestore(&drm_minor_lock, flags);
+       minor->index = 0;
+
        drm_debugfs_cleanup(minor);
        drm_sysfs_device_remove(minor);
-       idr_remove(&drm_minors_idr, minor->index);
 }
 
 /**
@@ -361,12 +391,21 @@ static void drm_minor_unregister(struct drm_device *dev, unsigned int type)
 struct drm_minor *drm_minor_acquire(unsigned int minor_id)
 {
        struct drm_minor *minor;
+       unsigned long flags;
 
+       spin_lock_irqsave(&drm_minor_lock, flags);
        minor = idr_find(&drm_minors_idr, minor_id);
-       if (!minor)
+       if (minor)
+               drm_dev_ref(minor->dev);
+       spin_unlock_irqrestore(&drm_minor_lock, flags);
+
+       if (!minor) {
+               return ERR_PTR(-ENODEV);
+       } else if (drm_device_is_unplugged(minor->dev)) {
+               drm_dev_unref(minor->dev);
                return ERR_PTR(-ENODEV);
+       }
 
-       drm_dev_ref(minor->dev);
        return minor;
 }