amdgpu: Replace idr with xarray in amdgpu_bo_list

Tvrtko Ursulin Fri, 19 Dec 2025 01:09:00 -0800


On 19/12/2025 07:57, Christian König wrote:

On 12/18/25 16:04, Tvrtko Ursulin wrote:

IDR is deprecated so let's replace it with xarray.

Conversion is mostly 1:1 apart from AMDGPU_BO_LIST_OP_UPDATE which was
implemented with idr_replace, and has now been replaced with a sequence of
xa_load and xa_cmpxchg. Should userspace attempt multi-threaded update
operations on the same handle it could theoretically hit a new -ENOENT
path. But I believe this is purely theoretical and still safe.

Signed-off-by: Tvrtko Ursulin <[email protected]>
---
  drivers/gpu/drm/amd/amdgpu/amdgpu.h         |  4 +-
  drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c | 72 ++++++++++-----------
  drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.h |  2 +-
  drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c     | 11 ++--
  4 files changed, 41 insertions(+), 48 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu.h 
b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
index 9f9774f58ce1..0a5b802bd3c3 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
@@ -50,6 +50,7 @@
  #include <linux/hashtable.h>
  #include <linux/dma-fence.h>
  #include <linux/pci.h>
+#include <linux/xarray.h>

#include <drm/ttm/ttm_bo.h>

  #include <drm/ttm/ttm_placement.h>
@@ -500,8 +501,7 @@ struct amdgpu_fpriv {
        struct amdgpu_bo_va     *prt_va;
        struct amdgpu_bo_va     *csa_va;
        struct amdgpu_bo_va     *seq64_va;
-       struct mutex            bo_list_lock;
-       struct idr              bo_list_handles;
+       struct xarray           bo_list_handles;
        struct amdgpu_ctx_mgr   ctx_mgr;
        struct amdgpu_userq_mgr userq_mgr;

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c

index 66fb37b64388..628d32fd2fae 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c
@@ -149,31 +149,20 @@ int amdgpu_bo_list_create(struct amdgpu_device *adev, 
struct drm_file *filp,

}-static void amdgpu_bo_list_destroy(struct amdgpu_fpriv *fpriv, int id)

-{
-       struct amdgpu_bo_list *list;
-
-       mutex_lock(&fpriv->bo_list_lock);
-       list = idr_remove(&fpriv->bo_list_handles, id);
-       mutex_unlock(&fpriv->bo_list_lock);
-       if (list)
-               kref_put(&list->refcount, amdgpu_bo_list_free);
-}
-
-int amdgpu_bo_list_get(struct amdgpu_fpriv *fpriv, int id,
+int amdgpu_bo_list_get(struct amdgpu_fpriv *fpriv, u32 id,
                       struct amdgpu_bo_list **result)
  {
-       rcu_read_lock();
-       *result = idr_find(&fpriv->bo_list_handles, id);
+       struct amdgpu_bo_list *list;

- if (*result && kref_get_unless_zero(&(*result)->refcount)) {

-               rcu_read_unlock();
-               return 0;
-       }
+       xa_lock(&fpriv->bo_list_handles);
+       list = xa_load(&fpriv->bo_list_handles, id);
+       if (list && !kref_get_unless_zero(&list->refcount))
+               list = NULL;


Since you have this protected by xa_lock() now you don't need the 
kref_get_unless_zero() any more and can also drop the RCU handling in 
amdgpu_bo_list_free().

Alternatively stop using xa_lock() and use the RCU read side lock instead, but 
I clearly prefer this approach here.


True, ok.


Apart from that looks good to me.

Btw what about the bo_list_mutex? CS parsing looks to be read only withrespect to the bo_list so what it is protecting?


Regards,

Tvrtko

+       xa_unlock(&fpriv->bo_list_handles);

- rcu_read_unlock();

-       *result = NULL;
-       return -ENOENT;
+       *result = list;
+
+       return list ? 0 : -ENOENT;
  }

void amdgpu_bo_list_put(struct amdgpu_bo_list *list)

@@ -219,12 +208,12 @@ int amdgpu_bo_create_list_entry_array(struct 
drm_amdgpu_bo_list_in *in,
  int amdgpu_bo_list_ioctl(struct drm_device *dev, void *data,
                                struct drm_file *filp)
  {
-       struct amdgpu_device *adev = drm_to_adev(dev);
        struct amdgpu_fpriv *fpriv = filp->driver_priv;
-       union drm_amdgpu_bo_list *args = data;
-       uint32_t handle = args->in.list_handle;
+       struct amdgpu_device *adev = drm_to_adev(dev);
        struct drm_amdgpu_bo_list_entry *info = NULL;
-       struct amdgpu_bo_list *list, *old;
+       struct amdgpu_bo_list *list, *prev, *curr;
+       uint32_t handle = args->in.list_handle;
+       union drm_amdgpu_bo_list *args = data;
        int r;

r = amdgpu_bo_create_list_entry_array(&args->in, &info);

@@ -238,19 +227,19 @@ int amdgpu_bo_list_ioctl(struct drm_device *dev, void 
*data,
                if (r)
                        goto error_free;

- mutex_lock(&fpriv->bo_list_lock);

-               r = idr_alloc(&fpriv->bo_list_handles, list, 1, 0, GFP_KERNEL);
-               mutex_unlock(&fpriv->bo_list_lock);
-               if (r < 0) {
+               r = xa_alloc(&fpriv->bo_list_handles, &handle, list,
+                            xa_limit_32b, GFP_KERNEL);
+               if (r)
                        goto error_put_list;
-               }

- handle = r;

                break;

case AMDGPU_BO_LIST_OP_DESTROY:

-               amdgpu_bo_list_destroy(fpriv, handle);
+               list = xa_erase(&fpriv->bo_list_handles, handle);
+               if (list)
+                       amdgpu_bo_list_put(list);
                handle = 0;
+
                break;

case AMDGPU_BO_LIST_OP_UPDATE:

@@ -259,16 +248,23 @@ int amdgpu_bo_list_ioctl(struct drm_device *dev, void 
*data,
                if (r)
                        goto error_free;

- mutex_lock(&fpriv->bo_list_lock);

-               old = idr_replace(&fpriv->bo_list_handles, list, handle);
-               mutex_unlock(&fpriv->bo_list_lock);
+               curr = xa_load(&fpriv->bo_list_handles, handle);
+               if (!curr) {
+                       r = -ENOENT;
+                       goto error_put_list;
+               }

- if (IS_ERR(old)) {

-                       r = PTR_ERR(old);
+               prev = xa_cmpxchg(&fpriv->bo_list_handles, handle, curr, list,
+                                 GFP_KERNEL);
+               if (xa_is_err(prev)) {
+                       r = xa_err(prev);
+                       goto error_put_list;
+               } else if (prev != curr) {
+                       r = -ENOENT;
                        goto error_put_list;
                }

- amdgpu_bo_list_put(old);

+               amdgpu_bo_list_put(curr);
                break;

default:

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.h 
b/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.h
index 2b5e7c46a39d..0989f1090c63 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.h
@@ -58,7 +58,7 @@ struct amdgpu_bo_list {
        struct amdgpu_bo_list_entry entries[] __counted_by(num_entries);
  };

-int amdgpu_bo_list_get(struct amdgpu_fpriv *fpriv, int id,

+int amdgpu_bo_list_get(struct amdgpu_fpriv *fpriv, u32 id,
                       struct amdgpu_bo_list **result);
  void amdgpu_bo_list_put(struct amdgpu_bo_list *list);
  int amdgpu_bo_create_list_entry_array(struct drm_amdgpu_bo_list_in *in,
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c 
b/drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c
index 6ee77f431d56..88f104041157 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c
@@ -1445,8 +1445,7 @@ int amdgpu_driver_open_kms(struct drm_device *dev, struct 
drm_file *file_priv)
        if (r)
                goto error_vm;

- mutex_init(&fpriv->bo_list_lock);

-       idr_init_base(&fpriv->bo_list_handles, 1);
+       xa_init_flags(&fpriv->bo_list_handles, XA_FLAGS_ALLOC1);

r = amdgpu_userq_mgr_init(&fpriv->userq_mgr, file_priv, adev);

        if (r)
@@ -1492,8 +1491,8 @@ void amdgpu_driver_postclose_kms(struct drm_device *dev,
        struct amdgpu_fpriv *fpriv = file_priv->driver_priv;
        struct amdgpu_bo_list *list;
        struct amdgpu_bo *pd;
+       unsigned long handle;
        u32 pasid;
-       int handle;

if (!fpriv)

                return;
@@ -1529,11 +1528,9 @@ void amdgpu_driver_postclose_kms(struct drm_device *dev,
                amdgpu_pasid_free_delayed(pd->tbo.base.resv, pasid);
        amdgpu_bo_unref(&pd);

- idr_for_each_entry(&fpriv->bo_list_handles, list, handle)

+       xa_for_each(&fpriv->bo_list_handles, handle, list)
                amdgpu_bo_list_put(list);
-
-       idr_destroy(&fpriv->bo_list_handles);
-       mutex_destroy(&fpriv->bo_list_lock);
+       xa_destroy(&fpriv->bo_list_handles);

kfree(fpriv);

        file_priv->driver_priv = NULL;

Re: [RFC 1/5] drm/amdgpu: Replace idr with xarray in amdgpu_bo_list

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