[PATCH v2 0/2] drm: Use full allocated minor range for DRM

[PATCH v2 0/2] drm: Use full allocated minor range for DRM

[Michał Winiarski]

64 DRM device nodes is not enough for everyone.
Upgrade it to ~341K (which definitely is more than enough).
Additionally - one minor tweak around minor IDR locking.

v1 -> v2:
Don't touch DRM_MINOR_CONTROL and its range (Simon Ser)

Michał Winiarski (2):
  drm: Expand max DRM device number to full MINORBITS
  drm: Use mutex for minors

 drivers/gpu/drm/drm_drv.c | 45 ++++++++++++++++++---------------------
 1 file changed, 21 insertions(+), 24 deletions(-)

-- 
2.37.2

[PATCH v2 1/2] drm: Expand max DRM device number to full MINORBITS

[Michał Winiarski]

Having a limit of 64 DRM devices is not good enough for modern world
where we have multi-GPU servers, SR-IOV virtual functions and virtual
devices used for testing.
Let's utilize full minor range for DRM devices.
To avoid regressing the existing userspace, we're still maintaining the
numbering scheme where 0-63 is used for primary, 64-127 is reserved
(formerly for control) and 128-191 is used for render.
This is continued for minors >= 192 (192-255 for primary, 256-319
reserved, 320-383 for render, and so on).

Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
---
 drivers/gpu/drm/drm_drv.c | 24 ++++++++++++++----------
 1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index 8214a0b1ab7f..b64b5c45cd80 100644
--- a/drivers/gpu/drm/drm_drv.c
+++ b/drivers/gpu/drm/drm_drv.c
@@ -113,7 +113,7 @@ static int drm_minor_alloc(struct drm_device *dev, unsigned int type)
 {
 	struct drm_minor *minor;
 	unsigned long flags;
-	int r;
+	int r, start, end;
 
 	minor = drmm_kzalloc(dev, sizeof(*minor), GFP_KERNEL);
 	if (!minor)
@@ -122,15 +122,19 @@ 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();
+	start = 64 * type;
+	end = 64 * (type + 1);
+
+	do {
+		idr_preload(GFP_KERNEL);
+		spin_lock_irqsave(&drm_minor_lock, flags);
+		r = idr_alloc(&drm_minors_idr, NULL, start, end, GFP_NOWAIT);
+		spin_unlock_irqrestore(&drm_minor_lock, flags);
+		idr_preload_end();
+
+		start += 192;
+		end += 192;
+	} while ((r == -ENOSPC) && end <= (1 << MINORBITS));
 
 	if (r < 0)
 		return r;
-- 
2.37.2

Re: [PATCH v2 1/2] drm: Expand max DRM device number to full MINORBITS

[Simon Ser]

This approach will not break existing user-space AFAIK.

Acked-by: Simon Ser <contact@emersion.fr>

[PATCH v2 2/2] drm: Use mutex for minors

[Michał Winiarski]

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@intel.com>
---
 drivers/gpu/drm/drm_drv.c | 31 ++++++++++++-------------------
 1 file changed, 12 insertions(+), 19 deletions(-)

diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index b64b5c45cd80..8706d846abb7 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;
 
 /*
@@ -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);
+	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, start, end;
 
 	minor = drmm_kzalloc(dev, sizeof(*minor), GFP_KERNEL);
@@ -126,11 +124,9 @@ static int drm_minor_alloc(struct drm_device *dev, unsigned int type)
 	end = 64 * (type + 1);
 
 	do {
-		idr_preload(GFP_KERNEL);
-		spin_lock_irqsave(&drm_minor_lock, flags);
-		r = idr_alloc(&drm_minors_idr, NULL, start, end, GFP_NOWAIT);
-		spin_unlock_irqrestore(&drm_minor_lock, flags);
-		idr_preload_end();
+		mutex_lock(&drm_minor_lock);
+		r = idr_alloc(&drm_minors_idr, NULL, start, end, GFP_KERNEL);
+		mutex_unlock(&drm_minor_lock);
 
 		start += 192;
 		end += 192;
@@ -156,7 +152,6 @@ 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");
@@ -176,9 +171,9 @@ 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;
@@ -191,16 +186,15 @@ 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 */
@@ -219,13 +213,12 @@ 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);
-- 
2.37.2