Re: [PATCH v4 1/3] drm: Use XArray instead of IDR for minors
On Tue, Sep 06, 2022 at 10:02:24PM +0100, Matthew Wilcox wrote:
> On Tue, Sep 06, 2022 at 10:16:27PM +0200, 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
> > Suggested-by: Matthew Wilcox
>
> I have a few questions, but I like where you're going.
>
> > @@ -98,21 +98,18 @@ 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_release(&drm_minors_xa, minor->index);
>
> Has it definitely been unused at this point? I would think that
> xa_erase() (an unconditional store) would be the correct function to
> call.
Yes, unless there's a programmers error somewhere - I'll replace it though.
>
> > @@ -122,20 +119,12 @@ 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, &id, NULL,
> > +XA_LIMIT(64 * type, 64 * (type + 1) - 1), GFP_KERNEL);
> > if (r < 0)
> > return r;
> >
> > - minor->index = r;
> > + minor->index = id;
>
> Wouldn't it be better to call:
>
> r = xa_alloc(&drm_minors_xa, &minor->index, NULL,
> XA_LIMIT(64 * type, 64 * (type + 1) - 1), GFP_KERNEL);
>
> I might also prefer a little syntactic sugar like:
>
> #define DRM_MINOR_LIMIT(type) XA_LIMIT(64 * (type), 64 * (type) + 63)
>
> but that's definitely a matter of taste.
Sure.
>
> > @@ -172,9 +161,12 @@ 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);
>
> Might be better as an xa_cmpxchg()?
Ack.
>
> > @@ -187,16 +179,13 @@ 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_erase(&drm_minors_xa, minor->index);
>
> This isn't an exact replacement, but I'm not sure whether that makes a
> difference. xa_erase() allows allocation of this ID again while
> idr_replace() means that lookups return NULL, but the ID remains in
> use. The equivalent of idr_replace() is:
> xa_store(&drm_minors_xa, minor->index, NULL, GFP_KERNEL);
It does makes a difference, I'll change it to the equivalent.
>
> > @@ -215,13 +204,10 @@ 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);
> > + minor = xa_load(&drm_minors_xa, minor_id);
> > if (minor)
> > drm_dev_get(minor->dev);
> > - spin_unlock_irqrestore(&drm_minor_lock, flags);
>
> This is also not an exact equivalent as the dev_drm_get() is now outside
> the lock. Does that matter in this case? I don't know the code well
> enough to say. If you want it to be equivalent, then:
>
> xa_lock(&drm_minors_xa);
> minor = xa_load(&drm_minors_xa, minor_id);
> if (minor)
> drm_dev_get(minor->dev);
> xa_unlock(&drm_
Re: [PATCH v4 1/3] drm: Use XArray instead of IDR for minors
On Tue, Sep 06, 2022 at 10:16:27PM +0200, 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
> Suggested-by: Matthew Wilcox
I have a few questions, but I like where you're going.
> @@ -98,21 +98,18 @@ 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_release(&drm_minors_xa, minor->index);
Has it definitely been unused at this point? I would think that
xa_erase() (an unconditional store) would be the correct function to
call.
> @@ -122,20 +119,12 @@ 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, &id, NULL,
> + XA_LIMIT(64 * type, 64 * (type + 1) - 1), GFP_KERNEL);
> if (r < 0)
> return r;
>
> - minor->index = r;
> + minor->index = id;
Wouldn't it be better to call:
r = xa_alloc(&drm_minors_xa, &minor->index, NULL,
XA_LIMIT(64 * type, 64 * (type + 1) - 1), GFP_KERNEL);
I might also prefer a little syntactic sugar like:
#define DRM_MINOR_LIMIT(type) XA_LIMIT(64 * (type), 64 * (type) + 63)
but that's definitely a matter of taste.
> @@ -172,9 +161,12 @@ 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);
Might be better as an xa_cmpxchg()?
> @@ -187,16 +179,13 @@ 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_erase(&drm_minors_xa, minor->index);
This isn't an exact replacement, but I'm not sure whether that makes a
difference. xa_erase() allows allocation of this ID again while
idr_replace() means that lookups return NULL, but the ID remains in
use. The equivalent of idr_replace() is:
xa_store(&drm_minors_xa, minor->index, NULL, GFP_KERNEL);
> @@ -215,13 +204,10 @@ 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);
> + minor = xa_load(&drm_minors_xa, minor_id);
> if (minor)
> drm_dev_get(minor->dev);
> - spin_unlock_irqrestore(&drm_minor_lock, flags);
This is also not an exact equivalent as the dev_drm_get() is now outside
the lock. Does that matter in this case? I don't know the code well
enough to say. If you want it to be equivalent, then:
xa_lock(&drm_minors_xa);
minor = xa_load(&drm_minors_xa, minor_id);
if (minor)
drm_dev_get(minor->dev);
xa_unlock(&drm_minors_xa);
would be the code to use.
> @@ -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);
> + xa_destroy(&drm_minors_xa);
I don't know if this is the right call. xa_destroy() is the exa
[PATCH v4 1/3] drm: Use XArray instead of IDR for minors
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
Suggested-by: Matthew Wilcox
---
drivers/gpu/drm/drm_drv.c | 49 ++-
1 file changed, 17 insertions(+), 32 deletions(-)
diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index 8214a0b1ab7f..41799e4d0432 100644
--- a/drivers/gpu/drm/drm_drv.c
+++ b/drivers/gpu/drm/drm_drv.c
@@ -34,6 +34,7 @@
#include
#include
#include
+#include
#include
#include
@@ -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 +98,18 @@ 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_release(&drm_minors_xa, minor->index);
}
static int drm_minor_alloc(struct drm_device *dev, unsigned int type)
{
struct drm_minor *minor;
- unsigned long flags;
+ u32 id;
int r;
minor = drmm_kzalloc(dev, sizeof(*minor), GFP_KERNEL);
@@ -122,20 +119,12 @@ 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, &id, NULL,
+XA_LIMIT(64 * type, 64 * (type + 1) - 1), GFP_KERNEL);
if (r < 0)
return r;
- minor->index = r;
+ minor->index = id;
r = drmm_add_action_or_reset(dev, drm_minor_alloc_release, minor);
if (r)
@@ -152,7 +141,7 @@ 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 +161,12 @@ 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 +179,13 @@ 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_erase(&drm_minors_xa, minor->index);
device_del(minor->kdev);
dev_set_drvdata(minor->kdev, NULL); /* safety belt */
@@ -215,13 +204,10 @@ 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);
+ minor = xa_load(&drm_minors_xa, minor_id);
if (minor)
drm_dev_get(minor->dev);
- spin_unlock_irqrestore(&drm_minor_lock, flags);
if (!minor) {
return ERR_PTR(-ENODEV);
@@ -1037,7 +1023,7 @@ static void drm_core_exit(void)
unregister_chrdev(DRM_MAJOR, "drm");
debugfs_rem
