Re: [PATCH v6 1/4] drm: Use XArray instead of IDR for minors
From: James Zhu
Date: Tue Aug 29 2023 - 13:35:18 EST
On 2023-08-28 17:08, Michał Winiarski wrote:
On Fri, Aug 25, 2023 at 12:59:26PM -0400, James Zhu wrote:
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@xxxxxxxxx>
Suggested-by: Matthew Wilcox<willy@xxxxxxxxxxxxx>
---
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?
We expect NULL here.
The same one that was previously stored here ⌄⌄⌄
r = xa_alloc(&drm_minors_xa, &minor->index, NULL, DRM_EXTENDED_MINOR_LIMIT, GFP_KERNEL);
in drm_minor_alloc.
[JZ] My mistake.
}
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?
We're relying on the ordering for acquire/release (previously
guaranteed by the drm_minor_lock, now by internal XArray locking).
xa_load doesn't take xa_lock internally:
https://docs.kernel.org/core-api/xarray.html#locking
[JZ] I means that drm_dev_get(minor->dev); can move out of xa_lock.
- 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?
We could, if we expect the xarray to potentially not be empty.
From what I understand - all minors should be released at this point.
[JZ] In practice, adding destroy here will be better.
Thanks,
-Michał
+ 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();