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_stub.c b/drivers/gpu/drm/drm_stub.c
index 83ef4a6..c23eaf6 100644
--- a/drivers/gpu/drm/drm_stub.c
+++ b/drivers/gpu/drm/drm_stub.c
@@ -70,6 +70,7 @@
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 @@
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 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 @@
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 @@
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 @@
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)
- return ERR_PTR(-ENODEV);
+ if (minor)
+ drm_dev_ref(minor->dev);
+ spin_unlock_irqrestore(&drm_minor_lock, flags);
- drm_dev_ref(minor->dev);
+ if (!minor) {
+ return ERR_PTR(-ENODEV);
+ } else if (drm_device_is_unplugged(minor->dev)) {
+ drm_dev_unref(minor->dev);
+ return ERR_PTR(-ENODEV);
+ }
+
return minor;
}