[Intel-gfx] [PATCH v6 1/4] drm: Use XArray instead of IDR for minors

James Zhu jamesz at amd.com
Fri Aug 25 16:59:26 UTC 2023


On 2023-07-24 17:14, Michał Winiarski wrote:
> 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 at intel.com>
> Suggested-by: Matthew Wilcox<willy at infradead.org>
> ---
>   drivers/gpu/drm/drm_drv.c | 63 ++++++++++++++++-----------------------
>   1 file changed, 25 insertions(+), 38 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> index 3eda026ffac6..3faecb01186f 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_accel.h>
>   #include <drm/drm_cache.h>
> @@ -54,8 +55,7 @@ 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,
> @@ -101,26 +101,23 @@ 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);
>   
> -	if (minor->type == DRM_MINOR_ACCEL) {
> +	if (minor->type == DRM_MINOR_ACCEL)
>   		accel_minor_remove(minor->index);
> -	} else {
> -		spin_lock_irqsave(&drm_minor_lock, flags);
> -		idr_remove(&drm_minors_idr, minor->index);
> -		spin_unlock_irqrestore(&drm_minor_lock, flags);
> -	}
> +	else
> +		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, enum drm_minor_type type)
>   {
>   	struct drm_minor *minor;
> -	unsigned long flags;
> -	int r;
> +	int index, r;
>   
>   	minor = drmm_kzalloc(dev, sizeof(*minor), GFP_KERNEL);
>   	if (!minor)
> @@ -129,24 +126,17 @@ static int drm_minor_alloc(struct drm_device *dev, enum drm_minor_type type)
>   	minor->type = type;
>   	minor->dev = dev;
>   
> -	idr_preload(GFP_KERNEL);
>   	if (type == DRM_MINOR_ACCEL) {
>   		r = accel_minor_alloc();
> +		index = r;
>   	} else {
> -		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);
> +		r = xa_alloc(&drm_minors_xa, &index, NULL, DRM_MINOR_LIMIT(type), GFP_KERNEL);
>   	}
> -	idr_preload_end();
>   
>   	if (r < 0)
>   		return r;
>   
> -	minor->index = r;
> +	minor->index = index;
>   
>   	r = drmm_add_action_or_reset(dev, drm_minor_alloc_release, minor);
>   	if (r)
> @@ -163,7 +153,7 @@ static int drm_minor_alloc(struct drm_device *dev, enum drm_minor_type type)
>   static int drm_minor_register(struct drm_device *dev, enum drm_minor_type type)
>   {
>   	struct drm_minor *minor;
> -	unsigned long flags;
> +	void *entry;
>   	int ret;
>   
>   	DRM_DEBUG("\n");
> @@ -190,9 +180,12 @@ static int drm_minor_register(struct drm_device *dev, enum drm_minor_type type)
>   	if (minor->type == DRM_MINOR_ACCEL) {
>   		accel_minor_replace(minor, minor->index);
>   	} else {
> -		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);
[JZ] would WARN_ON(entry != minor)be better?
>   	}
>   
>   	DRM_DEBUG("new minor registered %d\n", minor->index);
> @@ -206,20 +199,16 @@ static int drm_minor_register(struct drm_device *dev, enum drm_minor_type type)
>   static void drm_minor_unregister(struct drm_device *dev, enum drm_minor_type 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 */
> -	if (minor->type == DRM_MINOR_ACCEL) {
> +	if (minor->type == DRM_MINOR_ACCEL)
>   		accel_minor_replace(NULL, minor->index);
> -	} else {
> -		spin_lock_irqsave(&drm_minor_lock, flags);
> -		idr_replace(&drm_minors_idr, NULL, minor->index);
> -		spin_unlock_irqrestore(&drm_minor_lock, flags);
> -	}
> +	else
> +		xa_store(&drm_minors_xa, minor->index, NULL, GFP_KERNEL);
>   
>   	device_del(minor->kdev);
>   	dev_set_drvdata(minor->kdev, NULL); /* safety belt */
> @@ -238,13 +227,12 @@ static void drm_minor_unregister(struct drm_device *dev, enum drm_minor_type typ
>   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);
[JZ] why minor->dev need ca_lock here?
> -	spin_unlock_irqrestore(&drm_minor_lock, flags);
> +	xa_unlock(&drm_minors_xa);
>   
>   	if (!minor) {
>   		return ERR_PTR(-ENODEV);
> @@ -1067,7 +1055,7 @@ static void drm_core_exit(void)
>   	unregister_chrdev(DRM_MAJOR, "drm");
>   	debugfs_remove(drm_debugfs_root);
>   	drm_sysfs_destroy();
> -	idr_destroy(&drm_minors_idr);
[JZ] Should we call xa_destroy instead here?
> +	WARN_ON(!xa_empty(&drm_minors_xa));
>   	drm_connector_ida_destroy();
>   }
>   
> @@ -1076,7 +1064,6 @@ 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();
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