linux-kernel - [PATCH v3 3/4] drm: Use mutex for minors

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Message-ID: <20220906140117.409852-4-michal.winiarski@intel.com>
Date:   Tue, 6 Sep 2022 16:01:16 +0200
From:   Michał Winiarski <michal.winiarski@...el.com>
To:     <dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>
CC:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        "Maarten Lankhorst" <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Simon Ser <contact@...rsion.fr>,
        Matthew Wilcox <willy@...radead.org>,
        Michał Winiarski <michal.winiarski@...el.com>,
        "Daniel Vetter" <daniel.vetter@...ll.ch>
Subject: [PATCH v3 3/4] drm: Use mutex for minors

Operating on drm minor is not done in IRQ context, which means that we
could safely downgrade to regular non-irq spinlock.
But we can also go further and drop the idr_preload tricks by just using
a mutex.

Signed-off-by: Michał Winiarski <michal.winiarski@...el.com>
Reviewed-by: Daniel Vetter <daniel.vetter@...ll.ch>
---
 drivers/gpu/drm/drm_drv.c | 33 +++++++++++++--------------------
 1 file changed, 13 insertions(+), 20 deletions(-)

diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index 0bdcca0db611..f66904527256 100644
--- a/drivers/gpu/drm/drm_drv.c
+++ b/drivers/gpu/drm/drm_drv.c
@@ -53,7 +53,7 @@ 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 DEFINE_MUTEX(drm_minor_lock);
 static struct idr drm_minors_idr;
 
 static bool skip_legacy_minors;
@@ -103,21 +103,19 @@ 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);
+	mutex_lock(&drm_minor_lock);
 	idr_remove(&drm_minors_idr, minor->index);
-	spin_unlock_irqrestore(&drm_minor_lock, flags);
+	mutex_unlock(&drm_minor_lock);
 }
 
 static int drm_minor_alloc(struct drm_device *dev, unsigned int type)
 {
 	struct drm_minor *minor;
-	unsigned long flags;
 	int r = -ENOSPC;
 
 	minor = drmm_kzalloc(dev, sizeof(*minor), GFP_KERNEL);
@@ -133,18 +131,16 @@ static int drm_minor_alloc(struct drm_device *dev, unsigned int type)
 	 * and 128-191 are render nodes.
 	 * After reaching the limit, we're allocating minors dynamically - first-come, first-serve.
 	 */
-	idr_preload(GFP_KERNEL);
-	spin_lock_irqsave(&drm_minor_lock, flags);
+	mutex_lock(&drm_minor_lock);
 	if (!skip_legacy_minors)
 		r = idr_alloc(&drm_minors_idr,
 			      NULL,
 			      64 * type,
 			      64 * (type + 1),
-			      GFP_NOWAIT);
+			      GFP_KERNEL);
 	if (r == -ENOSPC)
-		r = idr_alloc(&drm_minors_idr, NULL, 192, 1 << MINORBITS, GFP_NOWAIT);
-	spin_unlock_irqrestore(&drm_minor_lock, flags);
-	idr_preload_end();
+		r = idr_alloc(&drm_minors_idr, NULL, 192, 1 << MINORBITS, GFP_KERNEL);
+	mutex_unlock(&drm_minor_lock);
 
 	if (r < 0)
 		return r;
@@ -166,7 +162,6 @@ 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;
 	int ret;
 
 	DRM_DEBUG("\n");
@@ -186,9 +181,9 @@ 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);
+	mutex_lock(&drm_minor_lock);
 	idr_replace(&drm_minors_idr, minor, minor->index);
-	spin_unlock_irqrestore(&drm_minor_lock, flags);
+	mutex_unlock(&drm_minor_lock);
 
 	DRM_DEBUG("new minor registered %d\n", minor->index);
 	return 0;
@@ -201,16 +196,15 @@ 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);
+	mutex_lock(&drm_minor_lock);
 	idr_replace(&drm_minors_idr, NULL, minor->index);
-	spin_unlock_irqrestore(&drm_minor_lock, flags);
+	mutex_unlock(&drm_minor_lock);
 
 	device_del(minor->kdev);
 	dev_set_drvdata(minor->kdev, NULL); /* safety belt */
@@ -229,13 +223,12 @@ 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);
+	mutex_lock(&drm_minor_lock);
 	minor = idr_find(&drm_minors_idr, minor_id);
 	if (minor)
 		drm_dev_get(minor->dev);
-	spin_unlock_irqrestore(&drm_minor_lock, flags);
+	mutex_unlock(&drm_minor_lock);
 
 	if (!minor) {
 		return ERR_PTR(-ENODEV);
-- 
2.37.3