[PATCH v3] drm: Use XArray instead of IDR for minors

* [PATCH v3] drm: Use XArray instead of IDR for minors
@ 2022-11-07 17:48 ` Michał Winiarski
  0 siblings, 0 replies; 6+ messages in thread
From: Michał Winiarski @ 2022-11-07 17:48 UTC (permalink / raw)
  To: dri-devel, linux-kernel, intel-gfx
  Cc: David Airlie, Daniel Vetter, Maarten Lankhorst, Maxime Ripard,
	Thomas Zimmermann, Simon Ser, Matthew Wilcox, Oded Gabbay,
	Michał Winiarski

IDR is deprecated, and since XArray manages its own state with internal
locking, it simplifies the locking on DRM side.
Additionally, don't use the IRQ-safe variant, since operating on drm
minor is not done in IRQ context.

Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
Suggested-by: Matthew Wilcox <willy@infradead.org>
---
This was originally sent as v4/v5 in larger series:
https://lore.kernel.org/dri-devel/20220911211443.581481-2-michal.winiarski@intel.com/
v1 -> v2:
Fixed locking and corrected some misuse of XArray API (Matthew Wilcox)
v2 -> v3:
Store correct pointer, use xa_store rather than xa_cmpxchg (Oded Gabbay)

 drivers/gpu/drm/drm_drv.c | 51 ++++++++++++++-------------------------
 1 file changed, 18 insertions(+), 33 deletions(-)

diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index 8214a0b1ab7f..bdcdfeac76bf 100644
--- a/drivers/gpu/drm/drm_drv.c
+++ b/drivers/gpu/drm/drm_drv.c
@@ -34,6 +34,7 @@
 #include <linux/pseudo_fs.h>
 #include <linux/slab.h>
 #include <linux/srcu.h>
+#include <linux/xarray.h>
 
 #include <drm/drm_cache.h>
 #include <drm/drm_client.h>
@@ -53,8 +54,7 @@ MODULE_AUTHOR("Gareth Hughes, Leif Delgass, José Fonseca, Jon Smirl");
 MODULE_DESCRIPTION("DRM shared core routines");
 MODULE_LICENSE("GPL and additional rights");
 
-static DEFINE_SPINLOCK(drm_minor_lock);
-static struct idr drm_minors_idr;
+static DEFINE_XARRAY_ALLOC(drm_minors_xa);
 
 /*
  * If the drm core fails to init for whatever reason,
@@ -98,21 +98,19 @@ static struct drm_minor **drm_minor_get_slot(struct drm_device *dev,
 static void drm_minor_alloc_release(struct drm_device *dev, void *data)
 {
 	struct drm_minor *minor = data;
-	unsigned long flags;
 
 	WARN_ON(dev != minor->dev);
 
 	put_device(minor->kdev);
 
-	spin_lock_irqsave(&drm_minor_lock, flags);
-	idr_remove(&drm_minors_idr, minor->index);
-	spin_unlock_irqrestore(&drm_minor_lock, flags);
+	xa_erase(&drm_minors_xa, minor->index);
 }
 
+#define DRM_MINOR_LIMIT(t) ({ typeof(t) _t = (t); XA_LIMIT(64 * _t, 64 * _t + 63); })
+
 static int drm_minor_alloc(struct drm_device *dev, unsigned int type)
 {
 	struct drm_minor *minor;
-	unsigned long flags;
 	int r;
 
 	minor = drmm_kzalloc(dev, sizeof(*minor), GFP_KERNEL);
@@ -122,21 +120,10 @@ static int drm_minor_alloc(struct drm_device *dev, unsigned int type)
 	minor->type = type;
 	minor->dev = dev;
 
-	idr_preload(GFP_KERNEL);
-	spin_lock_irqsave(&drm_minor_lock, flags);
-	r = idr_alloc(&drm_minors_idr,
-		      NULL,
-		      64 * type,
-		      64 * (type + 1),
-		      GFP_NOWAIT);
-	spin_unlock_irqrestore(&drm_minor_lock, flags);
-	idr_preload_end();
-
+	r = xa_alloc(&drm_minors_xa, &minor->index, NULL, DRM_MINOR_LIMIT(type), GFP_KERNEL);
 	if (r < 0)
 		return r;
 
-	minor->index = r;
-
 	r = drmm_add_action_or_reset(dev, drm_minor_alloc_release, minor);
 	if (r)
 		return r;
@@ -152,7 +139,7 @@ static int drm_minor_alloc(struct drm_device *dev, unsigned int type)
 static int drm_minor_register(struct drm_device *dev, unsigned int type)
 {
 	struct drm_minor *minor;
-	unsigned long flags;
+	void *entry;
 	int ret;
 
 	DRM_DEBUG("\n");
@@ -172,9 +159,12 @@ 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, minor, minor->index);
-	spin_unlock_irqrestore(&drm_minor_lock, flags);
+	entry = xa_store(&drm_minors_xa, minor->index, minor, GFP_KERNEL);
+	if (xa_is_err(entry)) {
+		ret = xa_err(entry);
+		goto err_debugfs;
+	}
+	WARN_ON(entry);
 
 	DRM_DEBUG("new minor registered %d\n", minor->index);
 	return 0;
@@ -187,16 +177,13 @@ static int drm_minor_register(struct drm_device *dev, unsigned int type)
 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 || !device_is_registered(minor->kdev))
 		return;
 
 	/* replace @minor with NULL so lookups will fail from now on */
-	spin_lock_irqsave(&drm_minor_lock, flags);
-	idr_replace(&drm_minors_idr, NULL, minor->index);
-	spin_unlock_irqrestore(&drm_minor_lock, flags);
+	xa_store(&drm_minors_xa, minor->index, NULL, GFP_KERNEL);
 
 	device_del(minor->kdev);
 	dev_set_drvdata(minor->kdev, NULL); /* safety belt */
@@ -215,13 +202,12 @@ 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);
+	xa_lock(&drm_minors_xa);
+	minor = xa_load(&drm_minors_xa, minor_id);
 	if (minor)
 		drm_dev_get(minor->dev);
-	spin_unlock_irqrestore(&drm_minor_lock, flags);
+	xa_unlock(&drm_minors_xa);
 
 	if (!minor) {
 		return ERR_PTR(-ENODEV);
@@ -1037,7 +1023,7 @@ static void drm_core_exit(void)
 	unregister_chrdev(DRM_MAJOR, "drm");
 	debugfs_remove(drm_debugfs_root);
 	drm_sysfs_destroy();
-	idr_destroy(&drm_minors_idr);
+	WARN_ON(!xa_empty(&drm_minors_xa));
 	drm_connector_ida_destroy();
 }
 
@@ -1046,7 +1032,6 @@ static int __init drm_core_init(void)
 	int ret;
 
 	drm_connector_ida_init();
-	idr_init(&drm_minors_idr);
 	drm_memcpy_init_early();
 
 	ret = drm_sysfs_init();
-- 
2.38.1


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