[PATCH v2 1/2] drm/amdgpu/userq: refcount userqueues to avoid any race conditions

[PATCH v2 1/2] drm/amdgpu/userq: refcount userqueues to avoid any race conditions

[Sunil Khatri]

To avoid race condition and avoid UAF cases, implement kref
based queues and protect the below operations using xa lock
a. Getting a queue from xarray
b. Increment/Decrement it's refcount

Every time some one want to access a queue, always get via
amdgpu_userq_get to make sure we have locks in place and get
the object if active.

A userqueue is destroyed on the last refcount is dropped which
typically would be via IOCTL or during fini.

Signed-off-by: Sunil Khatri <sunil.khatri@amd.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_userq.c     | 85 ++++++++++++++-----
 drivers/gpu/drm/amd/amdgpu/amdgpu_userq.h     |  4 +
 .../gpu/drm/amd/amdgpu/amdgpu_userq_fence.c   | 10 ++-
 3 files changed, 76 insertions(+), 23 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.c
index e07b2082cf25..bd62c95eeaad 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.c
@@ -461,7 +461,6 @@ static void amdgpu_userq_cleanup(struct amdgpu_usermode_queue *queue,
 	uq_funcs->mqd_destroy(queue);
 	amdgpu_userq_fence_driver_free(queue);
 	/* Use interrupt-safe locking since IRQ handlers may access these XArrays */
-	xa_erase_irq(&uq_mgr->userq_xa, queue_id);
 	xa_erase_irq(&adev->userq_doorbell_xa, queue->doorbell_index);
 	queue->userq_mgr = NULL;
 	list_del(&queue->userq_va_list);
@@ -470,12 +469,6 @@ static void amdgpu_userq_cleanup(struct amdgpu_usermode_queue *queue,
 	up_read(&adev->reset_domain->sem);
 }
 
-static struct amdgpu_usermode_queue *
-amdgpu_userq_find(struct amdgpu_userq_mgr *uq_mgr, u32 qid)
-{
-	return xa_load(&uq_mgr->userq_xa, qid);
-}
-
 void
 amdgpu_userq_ensure_ev_fence(struct amdgpu_userq_mgr *uq_mgr,
 			     struct amdgpu_eviction_fence_mgr *evf_mgr)
@@ -625,22 +618,14 @@ amdgpu_userq_get_doorbell_index(struct amdgpu_userq_mgr *uq_mgr,
 }
 
 static int
-amdgpu_userq_destroy(struct drm_file *filp, u32 queue_id)
+amdgpu_userq_destroy(struct amdgpu_userq_mgr *uq_mgr, struct amdgpu_usermode_queue *queue,
+		     u32 queue_id)
 {
-	struct amdgpu_fpriv *fpriv = filp->driver_priv;
-	struct amdgpu_userq_mgr *uq_mgr = &fpriv->userq_mgr;
 	struct amdgpu_device *adev = uq_mgr->adev;
-	struct amdgpu_usermode_queue *queue;
 	int r = 0;
 
 	cancel_delayed_work_sync(&uq_mgr->resume_work);
 	mutex_lock(&uq_mgr->userq_mutex);
-	queue = amdgpu_userq_find(uq_mgr, queue_id);
-	if (!queue) {
-		drm_dbg_driver(adev_to_drm(uq_mgr->adev), "Invalid queue id to destroy\n");
-		mutex_unlock(&uq_mgr->userq_mutex);
-		return -EINVAL;
-	}
 	amdgpu_userq_wait_for_last_fence(queue);
 	/* Cancel any pending hang detection work and cleanup */
 	if (queue->hang_detect_fence) {
@@ -680,6 +665,38 @@ amdgpu_userq_destroy(struct drm_file *filp, u32 queue_id)
 	return r;
 }
 
+struct amdgpu_usermode_queue *amdgpu_userq_get(struct amdgpu_userq_mgr *uq_mgr, u32 qid)
+{
+	struct amdgpu_usermode_queue *queue;
+
+	xa_lock(&uq_mgr->userq_xa);
+	queue = xa_load(&uq_mgr->userq_xa, qid);
+	if (queue)
+		kref_get(&queue->refcount);
+
+	xa_unlock(&uq_mgr->userq_xa);
+	return queue;
+}
+
+void amdgpu_userq_put(struct amdgpu_userq_mgr *uq_mgr, u32 qid)
+{
+	struct amdgpu_usermode_queue *queue;
+
+	xa_lock(&uq_mgr->userq_xa);
+	queue = xa_load(&uq_mgr->userq_xa, qid);
+
+	if (queue && refcount_dec_and_test(&queue->refcount.refcount)) {
+		__xa_erase(&uq_mgr->userq_xa, qid);
+		xa_unlock(&uq_mgr->userq_xa);
+
+		if (amdgpu_userq_destroy(uq_mgr, queue, qid))
+			drm_file_err(uq_mgr->file, "Failed to destroy usermode queue\n");
+		return;
+	}
+
+	xa_unlock(&uq_mgr->userq_xa);
+}
+
 static int amdgpu_userq_priority_permit(struct drm_file *filp,
 					int priority)
 {
@@ -891,6 +908,8 @@ amdgpu_userq_create(struct drm_file *filp, union drm_amdgpu_userq *args)
 
 	args->out.queue_id = qid;
 	atomic_inc(&uq_mgr->userq_count[queue->queue_type]);
+	/* drop this refcount during queue destroy */
+	kref_init(&queue->refcount);
 
 unlock:
 	mutex_unlock(&uq_mgr->userq_mutex);
@@ -985,6 +1004,7 @@ int amdgpu_userq_ioctl(struct drm_device *dev, void *data,
 		       struct drm_file *filp)
 {
 	union drm_amdgpu_userq *args = data;
+	struct amdgpu_fpriv *fpriv = filp->driver_priv;
 	int r;
 
 	if (!amdgpu_userq_enabled(dev))
@@ -1001,9 +1021,7 @@ int amdgpu_userq_ioctl(struct drm_device *dev, void *data,
 		break;
 
 	case AMDGPU_USERQ_OP_FREE:
-		r = amdgpu_userq_destroy(filp, args->in.queue_id);
-		if (r)
-			drm_file_err(filp, "Failed to destroy usermode queue\n");
+		amdgpu_userq_put(&fpriv->userq_mgr, args->in.queue_id);
 		break;
 
 	default:
@@ -1023,16 +1041,23 @@ amdgpu_userq_restore_all(struct amdgpu_userq_mgr *uq_mgr)
 
 	/* Resume all the queues for this process */
 	xa_for_each(&uq_mgr->userq_xa, queue_id, queue) {
+		queue = amdgpu_userq_get(uq_mgr, queue_id);
+		if (!queue)
+			continue;
+
 		if (!amdgpu_userq_buffer_vas_mapped(queue)) {
 			drm_file_err(uq_mgr->file,
 				     "trying restore queue without va mapping\n");
 			queue->state = AMDGPU_USERQ_STATE_INVALID_VA;
+			amdgpu_userq_put(uq_mgr, queue_id);
 			continue;
 		}
 
 		r = amdgpu_userq_restore_helper(queue);
 		if (r)
 			ret = r;
+
+		amdgpu_userq_put(uq_mgr, queue_id);
 	}
 
 	if (ret)
@@ -1266,9 +1291,13 @@ amdgpu_userq_evict_all(struct amdgpu_userq_mgr *uq_mgr)
 	amdgpu_userq_detect_and_reset_queues(uq_mgr);
 	/* Try to unmap all the queues in this process ctx */
 	xa_for_each(&uq_mgr->userq_xa, queue_id, queue) {
+		queue = amdgpu_userq_get(uq_mgr, queue_id);
+		if (!queue)
+			continue;
 		r = amdgpu_userq_preempt_helper(queue);
 		if (r)
 			ret = r;
+		amdgpu_userq_put(uq_mgr, queue_id);
 	}
 
 	if (ret)
@@ -1301,16 +1330,24 @@ amdgpu_userq_wait_for_signal(struct amdgpu_userq_mgr *uq_mgr)
 	int ret;
 
 	xa_for_each(&uq_mgr->userq_xa, queue_id, queue) {
+		queue = amdgpu_userq_get(uq_mgr, queue_id);
+		if (!queue)
+			continue;
+
 		struct dma_fence *f = queue->last_fence;
 
-		if (!f || dma_fence_is_signaled(f))
+		if (!f || dma_fence_is_signaled(f)) {
+			amdgpu_userq_put(uq_mgr, queue_id);
 			continue;
+		}
 		ret = dma_fence_wait_timeout(f, true, msecs_to_jiffies(100));
 		if (ret <= 0) {
 			drm_file_err(uq_mgr->file, "Timed out waiting for fence=%llu:%llu\n",
 				     f->context, f->seqno);
+			amdgpu_userq_put(uq_mgr, queue_id);
 			return -ETIMEDOUT;
 		}
+		amdgpu_userq_put(uq_mgr, queue_id);
 	}
 
 	return 0;
@@ -1368,9 +1405,15 @@ void amdgpu_userq_mgr_fini(struct amdgpu_userq_mgr *userq_mgr)
 	mutex_lock(&userq_mgr->userq_mutex);
 	amdgpu_userq_detect_and_reset_queues(userq_mgr);
 	xa_for_each(&userq_mgr->userq_xa, queue_id, queue) {
+		queue = amdgpu_userq_get(userq_mgr, queue_id);
+		if (!queue)
+			continue;
 		amdgpu_userq_wait_for_last_fence(queue);
 		amdgpu_userq_unmap_helper(queue);
 		amdgpu_userq_cleanup(queue, queue_id);
+		amdgpu_userq_put(userq_mgr, queue_id);
+		/* Second put is for the reference taken in this function itself */
+		amdgpu_userq_put(userq_mgr, queue_id);
 	}
 
 	xa_destroy(&userq_mgr->userq_xa);
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.h
index f4d1d46ae15e..ec3ce485626d 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.h
@@ -74,6 +74,7 @@ struct amdgpu_usermode_queue {
 	struct dentry		*debugfs_queue;
 	struct delayed_work hang_detect_work;
 	struct dma_fence *hang_detect_fence;
+	struct kref		refcount;
 
 	struct list_head	userq_va_list;
 };
@@ -114,6 +115,9 @@ struct amdgpu_db_info {
 	struct amdgpu_userq_obj	*db_obj;
 };
 
+struct amdgpu_usermode_queue *amdgpu_userq_get(struct amdgpu_userq_mgr *uq_mgr, u32 qid);
+void amdgpu_userq_put(struct amdgpu_userq_mgr *uq_mgr, u32 qid);
+
 int amdgpu_userq_ioctl(struct drm_device *dev, void *data, struct drm_file *filp);
 
 int amdgpu_userq_mgr_init(struct amdgpu_userq_mgr *userq_mgr, struct drm_file *file_priv,
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_userq_fence.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_userq_fence.c
index 3c30512a6266..ba453361d2b4 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_userq_fence.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_userq_fence.c
@@ -521,7 +521,7 @@ int amdgpu_userq_signal_ioctl(struct drm_device *dev, void *data,
 		goto put_gobj_read;
 
 	/* Retrieve the user queue */
-	queue = xa_load(&userq_mgr->userq_xa, args->queue_id);
+	queue = amdgpu_userq_get(userq_mgr, args->queue_id);
 	if (!queue) {
 		r = -ENOENT;
 		goto put_gobj_write;
@@ -612,6 +612,9 @@ int amdgpu_userq_signal_ioctl(struct drm_device *dev, void *data,
 free_syncobj_handles:
 	kfree(syncobj_handles);
 
+	if (queue)
+		amdgpu_userq_put(userq_mgr, args->queue_id);
+
 	return r;
 }
 
@@ -863,7 +866,7 @@ int amdgpu_userq_wait_ioctl(struct drm_device *dev, void *data,
 		 */
 		num_fences = dma_fence_dedup_array(fences, num_fences);
 
-		waitq = xa_load(&userq_mgr->userq_xa, wait_info->waitq_id);
+		waitq = amdgpu_userq_get(userq_mgr, wait_info->waitq_id);
 		if (!waitq) {
 			r = -EINVAL;
 			goto free_fences;
@@ -947,5 +950,8 @@ int amdgpu_userq_wait_ioctl(struct drm_device *dev, void *data,
 free_syncobj_handles:
 	kfree(syncobj_handles);
 
+	if (waitq)
+		amdgpu_userq_put(userq_mgr, wait_info->waitq_id);
+
 	return r;
 }
-- 
2.34.1

[PATCH v2 2/2] drm/amdgpu/userq: remove the unused variable from cleanup fn

[Sunil Khatri]

Remove the queue_id which is no more needed in amdgpu_userq_cleanup
fn.

Signed-off-by: Sunil Khatri <sunil.khatri@amd.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_userq.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.c
index bd62c95eeaad..2e54638af0d2 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.c
@@ -446,8 +446,7 @@ static int amdgpu_userq_wait_for_last_fence(struct amdgpu_usermode_queue *queue)
 	return ret;
 }
 
-static void amdgpu_userq_cleanup(struct amdgpu_usermode_queue *queue,
-				 u32 queue_id)
+static void amdgpu_userq_cleanup(struct amdgpu_usermode_queue *queue)
 {
 	struct amdgpu_userq_mgr *uq_mgr = queue->userq_mgr;
 	struct amdgpu_device *adev = uq_mgr->adev;
@@ -657,7 +656,7 @@ amdgpu_userq_destroy(struct amdgpu_userq_mgr *uq_mgr, struct amdgpu_usermode_que
 		drm_warn(adev_to_drm(uq_mgr->adev), "trying to destroy a HW mapping userq\n");
 		queue->state = AMDGPU_USERQ_STATE_HUNG;
 	}
-	amdgpu_userq_cleanup(queue, queue_id);
+	amdgpu_userq_cleanup(queue);
 	mutex_unlock(&uq_mgr->userq_mutex);
 
 	pm_runtime_put_autosuspend(adev_to_drm(adev)->dev);
@@ -1410,7 +1409,7 @@ void amdgpu_userq_mgr_fini(struct amdgpu_userq_mgr *userq_mgr)
 			continue;
 		amdgpu_userq_wait_for_last_fence(queue);
 		amdgpu_userq_unmap_helper(queue);
-		amdgpu_userq_cleanup(queue, queue_id);
+		amdgpu_userq_cleanup(queue);
 		amdgpu_userq_put(userq_mgr, queue_id);
 		/* Second put is for the reference taken in this function itself */
 		amdgpu_userq_put(userq_mgr, queue_id);
-- 
2.34.1

Re: [PATCH v2 1/2] drm/amdgpu/userq: refcount userqueues to avoid any race conditions

[Alex Deucher]

On Mon, Mar 2, 2026 at 1:09 PM Sunil Khatri <sunil.khatri@amd.com> wrote:
>
> To avoid race condition and avoid UAF cases, implement kref
> based queues and protect the below operations using xa lock
> a. Getting a queue from xarray
> b. Increment/Decrement it's refcount
>
> Every time some one want to access a queue, always get via
> amdgpu_userq_get to make sure we have locks in place and get
> the object if active.
>
> A userqueue is destroyed on the last refcount is dropped which
> typically would be via IOCTL or during fini.
>
> Signed-off-by: Sunil Khatri <sunil.khatri@amd.com>

Series is:
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>

> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_userq.c     | 85 ++++++++++++++-----
>  drivers/gpu/drm/amd/amdgpu/amdgpu_userq.h     |  4 +
>  .../gpu/drm/amd/amdgpu/amdgpu_userq_fence.c   | 10 ++-
>  3 files changed, 76 insertions(+), 23 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.c
> index e07b2082cf25..bd62c95eeaad 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.c
> @@ -461,7 +461,6 @@ static void amdgpu_userq_cleanup(struct amdgpu_usermode_queue *queue,
>         uq_funcs->mqd_destroy(queue);
>         amdgpu_userq_fence_driver_free(queue);
>         /* Use interrupt-safe locking since IRQ handlers may access these XArrays */
> -       xa_erase_irq(&uq_mgr->userq_xa, queue_id);
>         xa_erase_irq(&adev->userq_doorbell_xa, queue->doorbell_index);
>         queue->userq_mgr = NULL;
>         list_del(&queue->userq_va_list);
> @@ -470,12 +469,6 @@ static void amdgpu_userq_cleanup(struct amdgpu_usermode_queue *queue,
>         up_read(&adev->reset_domain->sem);
>  }
>
> -static struct amdgpu_usermode_queue *
> -amdgpu_userq_find(struct amdgpu_userq_mgr *uq_mgr, u32 qid)
> -{
> -       return xa_load(&uq_mgr->userq_xa, qid);
> -}
> -
>  void
>  amdgpu_userq_ensure_ev_fence(struct amdgpu_userq_mgr *uq_mgr,
>                              struct amdgpu_eviction_fence_mgr *evf_mgr)
> @@ -625,22 +618,14 @@ amdgpu_userq_get_doorbell_index(struct amdgpu_userq_mgr *uq_mgr,
>  }
>
>  static int
> -amdgpu_userq_destroy(struct drm_file *filp, u32 queue_id)
> +amdgpu_userq_destroy(struct amdgpu_userq_mgr *uq_mgr, struct amdgpu_usermode_queue *queue,
> +                    u32 queue_id)
>  {
> -       struct amdgpu_fpriv *fpriv = filp->driver_priv;
> -       struct amdgpu_userq_mgr *uq_mgr = &fpriv->userq_mgr;
>         struct amdgpu_device *adev = uq_mgr->adev;
> -       struct amdgpu_usermode_queue *queue;
>         int r = 0;
>
>         cancel_delayed_work_sync(&uq_mgr->resume_work);
>         mutex_lock(&uq_mgr->userq_mutex);
> -       queue = amdgpu_userq_find(uq_mgr, queue_id);
> -       if (!queue) {
> -               drm_dbg_driver(adev_to_drm(uq_mgr->adev), "Invalid queue id to destroy\n");
> -               mutex_unlock(&uq_mgr->userq_mutex);
> -               return -EINVAL;
> -       }
>         amdgpu_userq_wait_for_last_fence(queue);
>         /* Cancel any pending hang detection work and cleanup */
>         if (queue->hang_detect_fence) {
> @@ -680,6 +665,38 @@ amdgpu_userq_destroy(struct drm_file *filp, u32 queue_id)
>         return r;
>  }
>
> +struct amdgpu_usermode_queue *amdgpu_userq_get(struct amdgpu_userq_mgr *uq_mgr, u32 qid)
> +{
> +       struct amdgpu_usermode_queue *queue;
> +
> +       xa_lock(&uq_mgr->userq_xa);
> +       queue = xa_load(&uq_mgr->userq_xa, qid);
> +       if (queue)
> +               kref_get(&queue->refcount);
> +
> +       xa_unlock(&uq_mgr->userq_xa);
> +       return queue;
> +}
> +
> +void amdgpu_userq_put(struct amdgpu_userq_mgr *uq_mgr, u32 qid)
> +{
> +       struct amdgpu_usermode_queue *queue;
> +
> +       xa_lock(&uq_mgr->userq_xa);
> +       queue = xa_load(&uq_mgr->userq_xa, qid);
> +
> +       if (queue && refcount_dec_and_test(&queue->refcount.refcount)) {
> +               __xa_erase(&uq_mgr->userq_xa, qid);
> +               xa_unlock(&uq_mgr->userq_xa);
> +
> +               if (amdgpu_userq_destroy(uq_mgr, queue, qid))
> +                       drm_file_err(uq_mgr->file, "Failed to destroy usermode queue\n");
> +               return;
> +       }
> +
> +       xa_unlock(&uq_mgr->userq_xa);
> +}
> +
>  static int amdgpu_userq_priority_permit(struct drm_file *filp,
>                                         int priority)
>  {
> @@ -891,6 +908,8 @@ amdgpu_userq_create(struct drm_file *filp, union drm_amdgpu_userq *args)
>
>         args->out.queue_id = qid;
>         atomic_inc(&uq_mgr->userq_count[queue->queue_type]);
> +       /* drop this refcount during queue destroy */
> +       kref_init(&queue->refcount);
>
>  unlock:
>         mutex_unlock(&uq_mgr->userq_mutex);
> @@ -985,6 +1004,7 @@ int amdgpu_userq_ioctl(struct drm_device *dev, void *data,
>                        struct drm_file *filp)
>  {
>         union drm_amdgpu_userq *args = data;
> +       struct amdgpu_fpriv *fpriv = filp->driver_priv;
>         int r;
>
>         if (!amdgpu_userq_enabled(dev))
> @@ -1001,9 +1021,7 @@ int amdgpu_userq_ioctl(struct drm_device *dev, void *data,
>                 break;
>
>         case AMDGPU_USERQ_OP_FREE:
> -               r = amdgpu_userq_destroy(filp, args->in.queue_id);
> -               if (r)
> -                       drm_file_err(filp, "Failed to destroy usermode queue\n");
> +               amdgpu_userq_put(&fpriv->userq_mgr, args->in.queue_id);
>                 break;
>
>         default:
> @@ -1023,16 +1041,23 @@ amdgpu_userq_restore_all(struct amdgpu_userq_mgr *uq_mgr)
>
>         /* Resume all the queues for this process */
>         xa_for_each(&uq_mgr->userq_xa, queue_id, queue) {
> +               queue = amdgpu_userq_get(uq_mgr, queue_id);
> +               if (!queue)
> +                       continue;
> +
>                 if (!amdgpu_userq_buffer_vas_mapped(queue)) {
>                         drm_file_err(uq_mgr->file,
>                                      "trying restore queue without va mapping\n");
>                         queue->state = AMDGPU_USERQ_STATE_INVALID_VA;
> +                       amdgpu_userq_put(uq_mgr, queue_id);
>                         continue;
>                 }
>
>                 r = amdgpu_userq_restore_helper(queue);
>                 if (r)
>                         ret = r;
> +
> +               amdgpu_userq_put(uq_mgr, queue_id);
>         }
>
>         if (ret)
> @@ -1266,9 +1291,13 @@ amdgpu_userq_evict_all(struct amdgpu_userq_mgr *uq_mgr)
>         amdgpu_userq_detect_and_reset_queues(uq_mgr);
>         /* Try to unmap all the queues in this process ctx */
>         xa_for_each(&uq_mgr->userq_xa, queue_id, queue) {
> +               queue = amdgpu_userq_get(uq_mgr, queue_id);
> +               if (!queue)
> +                       continue;
>                 r = amdgpu_userq_preempt_helper(queue);
>                 if (r)
>                         ret = r;
> +               amdgpu_userq_put(uq_mgr, queue_id);
>         }
>
>         if (ret)
> @@ -1301,16 +1330,24 @@ amdgpu_userq_wait_for_signal(struct amdgpu_userq_mgr *uq_mgr)
>         int ret;
>
>         xa_for_each(&uq_mgr->userq_xa, queue_id, queue) {
> +               queue = amdgpu_userq_get(uq_mgr, queue_id);
> +               if (!queue)
> +                       continue;
> +
>                 struct dma_fence *f = queue->last_fence;
>
> -               if (!f || dma_fence_is_signaled(f))
> +               if (!f || dma_fence_is_signaled(f)) {
> +                       amdgpu_userq_put(uq_mgr, queue_id);
>                         continue;
> +               }
>                 ret = dma_fence_wait_timeout(f, true, msecs_to_jiffies(100));
>                 if (ret <= 0) {
>                         drm_file_err(uq_mgr->file, "Timed out waiting for fence=%llu:%llu\n",
>                                      f->context, f->seqno);
> +                       amdgpu_userq_put(uq_mgr, queue_id);
>                         return -ETIMEDOUT;
>                 }
> +               amdgpu_userq_put(uq_mgr, queue_id);
>         }
>
>         return 0;
> @@ -1368,9 +1405,15 @@ void amdgpu_userq_mgr_fini(struct amdgpu_userq_mgr *userq_mgr)
>         mutex_lock(&userq_mgr->userq_mutex);
>         amdgpu_userq_detect_and_reset_queues(userq_mgr);
>         xa_for_each(&userq_mgr->userq_xa, queue_id, queue) {
> +               queue = amdgpu_userq_get(userq_mgr, queue_id);
> +               if (!queue)
> +                       continue;
>                 amdgpu_userq_wait_for_last_fence(queue);
>                 amdgpu_userq_unmap_helper(queue);
>                 amdgpu_userq_cleanup(queue, queue_id);
> +               amdgpu_userq_put(userq_mgr, queue_id);
> +               /* Second put is for the reference taken in this function itself */
> +               amdgpu_userq_put(userq_mgr, queue_id);
>         }
>
>         xa_destroy(&userq_mgr->userq_xa);
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.h
> index f4d1d46ae15e..ec3ce485626d 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.h
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.h
> @@ -74,6 +74,7 @@ struct amdgpu_usermode_queue {
>         struct dentry           *debugfs_queue;
>         struct delayed_work hang_detect_work;
>         struct dma_fence *hang_detect_fence;
> +       struct kref             refcount;
>
>         struct list_head        userq_va_list;
>  };
> @@ -114,6 +115,9 @@ struct amdgpu_db_info {
>         struct amdgpu_userq_obj *db_obj;
>  };
>
> +struct amdgpu_usermode_queue *amdgpu_userq_get(struct amdgpu_userq_mgr *uq_mgr, u32 qid);
> +void amdgpu_userq_put(struct amdgpu_userq_mgr *uq_mgr, u32 qid);
> +
>  int amdgpu_userq_ioctl(struct drm_device *dev, void *data, struct drm_file *filp);
>
>  int amdgpu_userq_mgr_init(struct amdgpu_userq_mgr *userq_mgr, struct drm_file *file_priv,
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_userq_fence.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_userq_fence.c
> index 3c30512a6266..ba453361d2b4 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_userq_fence.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_userq_fence.c
> @@ -521,7 +521,7 @@ int amdgpu_userq_signal_ioctl(struct drm_device *dev, void *data,
>                 goto put_gobj_read;
>
>         /* Retrieve the user queue */
> -       queue = xa_load(&userq_mgr->userq_xa, args->queue_id);
> +       queue = amdgpu_userq_get(userq_mgr, args->queue_id);
>         if (!queue) {
>                 r = -ENOENT;
>                 goto put_gobj_write;
> @@ -612,6 +612,9 @@ int amdgpu_userq_signal_ioctl(struct drm_device *dev, void *data,
>  free_syncobj_handles:
>         kfree(syncobj_handles);
>
> +       if (queue)
> +               amdgpu_userq_put(userq_mgr, args->queue_id);
> +
>         return r;
>  }
>
> @@ -863,7 +866,7 @@ int amdgpu_userq_wait_ioctl(struct drm_device *dev, void *data,
>                  */
>                 num_fences = dma_fence_dedup_array(fences, num_fences);
>
> -               waitq = xa_load(&userq_mgr->userq_xa, wait_info->waitq_id);
> +               waitq = amdgpu_userq_get(userq_mgr, wait_info->waitq_id);
>                 if (!waitq) {
>                         r = -EINVAL;
>                         goto free_fences;
> @@ -947,5 +950,8 @@ int amdgpu_userq_wait_ioctl(struct drm_device *dev, void *data,
>  free_syncobj_handles:
>         kfree(syncobj_handles);
>
> +       if (waitq)
> +               amdgpu_userq_put(userq_mgr, wait_info->waitq_id);
> +
>         return r;
>  }
> --
> 2.34.1
>

Re: [PATCH v2 1/2] drm/amdgpu/userq: refcount userqueues to avoid any race conditions

[Christian König]

On 3/2/26 19:08, Sunil Khatri wrote:
> To avoid race condition and avoid UAF cases, implement kref
> based queues and protect the below operations using xa lock
> a. Getting a queue from xarray
> b. Increment/Decrement it's refcount
> 
> Every time some one want to access a queue, always get via
> amdgpu_userq_get to make sure we have locks in place and get
> the object if active.
> 
> A userqueue is destroyed on the last refcount is dropped which
> typically would be via IOCTL or during fini.
> 
> Signed-off-by: Sunil Khatri <sunil.khatri@amd.com>
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_userq.c     | 85 ++++++++++++++-----
>  drivers/gpu/drm/amd/amdgpu/amdgpu_userq.h     |  4 +
>  .../gpu/drm/amd/amdgpu/amdgpu_userq_fence.c   | 10 ++-
>  3 files changed, 76 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.c
> index e07b2082cf25..bd62c95eeaad 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.c
> @@ -461,7 +461,6 @@ static void amdgpu_userq_cleanup(struct amdgpu_usermode_queue *queue,
>  	uq_funcs->mqd_destroy(queue);
>  	amdgpu_userq_fence_driver_free(queue);
>  	/* Use interrupt-safe locking since IRQ handlers may access these XArrays */
> -	xa_erase_irq(&uq_mgr->userq_xa, queue_id);
>  	xa_erase_irq(&adev->userq_doorbell_xa, queue->doorbell_index);
>  	queue->userq_mgr = NULL;
>  	list_del(&queue->userq_va_list);
> @@ -470,12 +469,6 @@ static void amdgpu_userq_cleanup(struct amdgpu_usermode_queue *queue,
>  	up_read(&adev->reset_domain->sem);
>  }
>  
> -static struct amdgpu_usermode_queue *
> -amdgpu_userq_find(struct amdgpu_userq_mgr *uq_mgr, u32 qid)
> -{
> -	return xa_load(&uq_mgr->userq_xa, qid);
> -}
> -
>  void
>  amdgpu_userq_ensure_ev_fence(struct amdgpu_userq_mgr *uq_mgr,
>  			     struct amdgpu_eviction_fence_mgr *evf_mgr)
> @@ -625,22 +618,14 @@ amdgpu_userq_get_doorbell_index(struct amdgpu_userq_mgr *uq_mgr,
>  }
>  
>  static int
> -amdgpu_userq_destroy(struct drm_file *filp, u32 queue_id)
> +amdgpu_userq_destroy(struct amdgpu_userq_mgr *uq_mgr, struct amdgpu_usermode_queue *queue,
> +		     u32 queue_id)
>  {
> -	struct amdgpu_fpriv *fpriv = filp->driver_priv;
> -	struct amdgpu_userq_mgr *uq_mgr = &fpriv->userq_mgr;
>  	struct amdgpu_device *adev = uq_mgr->adev;
> -	struct amdgpu_usermode_queue *queue;
>  	int r = 0;
>  
>  	cancel_delayed_work_sync(&uq_mgr->resume_work);
>  	mutex_lock(&uq_mgr->userq_mutex);
> -	queue = amdgpu_userq_find(uq_mgr, queue_id);
> -	if (!queue) {
> -		drm_dbg_driver(adev_to_drm(uq_mgr->adev), "Invalid queue id to destroy\n");
> -		mutex_unlock(&uq_mgr->userq_mutex);
> -		return -EINVAL;
> -	}
>  	amdgpu_userq_wait_for_last_fence(queue);
>  	/* Cancel any pending hang detection work and cleanup */
>  	if (queue->hang_detect_fence) {
> @@ -680,6 +665,38 @@ amdgpu_userq_destroy(struct drm_file *filp, u32 queue_id)
>  	return r;
>  }
>  
> +struct amdgpu_usermode_queue *amdgpu_userq_get(struct amdgpu_userq_mgr *uq_mgr, u32 qid)
> +{
> +	struct amdgpu_usermode_queue *queue;
> +
> +	xa_lock(&uq_mgr->userq_xa);
> +	queue = xa_load(&uq_mgr->userq_xa, qid);
> +	if (queue)
> +		kref_get(&queue->refcount);
> +
> +	xa_unlock(&uq_mgr->userq_xa);
> +	return queue;
> +}
> +
> +void amdgpu_userq_put(struct amdgpu_userq_mgr *uq_mgr, u32 qid)
> +{
> +	struct amdgpu_usermode_queue *queue;
> +
> +	xa_lock(&uq_mgr->userq_xa);
> +	queue = xa_load(&uq_mgr->userq_xa, qid);
> +
> +	if (queue && refcount_dec_and_test(&queue->refcount.refcount)) {
> +		__xa_erase(&uq_mgr->userq_xa, qid);

That here makes no sense.

The queue id should be removed from the XA as soon as userspace uses AMDGPU_USERQ_OP_FREE and not when the last reference drops.

Regards,
Christian.

> +		xa_unlock(&uq_mgr->userq_xa);
> +
> +		if (amdgpu_userq_destroy(uq_mgr, queue, qid))
> +			drm_file_err(uq_mgr->file, "Failed to destroy usermode queue\n");
> +		return;
> +	}
> +
> +	xa_unlock(&uq_mgr->userq_xa);
> +}
> +
>  static int amdgpu_userq_priority_permit(struct drm_file *filp,
>  					int priority)
>  {
> @@ -891,6 +908,8 @@ amdgpu_userq_create(struct drm_file *filp, union drm_amdgpu_userq *args)
>  
>  	args->out.queue_id = qid;
>  	atomic_inc(&uq_mgr->userq_count[queue->queue_type]);
> +	/* drop this refcount during queue destroy */
> +	kref_init(&queue->refcount);
>  
>  unlock:
>  	mutex_unlock(&uq_mgr->userq_mutex);
> @@ -985,6 +1004,7 @@ int amdgpu_userq_ioctl(struct drm_device *dev, void *data,
>  		       struct drm_file *filp)
>  {
>  	union drm_amdgpu_userq *args = data;
> +	struct amdgpu_fpriv *fpriv = filp->driver_priv;
>  	int r;
>  
>  	if (!amdgpu_userq_enabled(dev))
> @@ -1001,9 +1021,7 @@ int amdgpu_userq_ioctl(struct drm_device *dev, void *data,
>  		break;
>  
>  	case AMDGPU_USERQ_OP_FREE:
> -		r = amdgpu_userq_destroy(filp, args->in.queue_id);
> -		if (r)
> -			drm_file_err(filp, "Failed to destroy usermode queue\n");
> +		amdgpu_userq_put(&fpriv->userq_mgr, args->in.queue_id);
>  		break;
>  
>  	default:
> @@ -1023,16 +1041,23 @@ amdgpu_userq_restore_all(struct amdgpu_userq_mgr *uq_mgr)
>  
>  	/* Resume all the queues for this process */
>  	xa_for_each(&uq_mgr->userq_xa, queue_id, queue) {
> +		queue = amdgpu_userq_get(uq_mgr, queue_id);
> +		if (!queue)
> +			continue;
> +
>  		if (!amdgpu_userq_buffer_vas_mapped(queue)) {
>  			drm_file_err(uq_mgr->file,
>  				     "trying restore queue without va mapping\n");
>  			queue->state = AMDGPU_USERQ_STATE_INVALID_VA;
> +			amdgpu_userq_put(uq_mgr, queue_id);
>  			continue;
>  		}
>  
>  		r = amdgpu_userq_restore_helper(queue);
>  		if (r)
>  			ret = r;
> +
> +		amdgpu_userq_put(uq_mgr, queue_id);
>  	}
>  
>  	if (ret)
> @@ -1266,9 +1291,13 @@ amdgpu_userq_evict_all(struct amdgpu_userq_mgr *uq_mgr)
>  	amdgpu_userq_detect_and_reset_queues(uq_mgr);
>  	/* Try to unmap all the queues in this process ctx */
>  	xa_for_each(&uq_mgr->userq_xa, queue_id, queue) {
> +		queue = amdgpu_userq_get(uq_mgr, queue_id);
> +		if (!queue)
> +			continue;
>  		r = amdgpu_userq_preempt_helper(queue);
>  		if (r)
>  			ret = r;
> +		amdgpu_userq_put(uq_mgr, queue_id);
>  	}
>  
>  	if (ret)
> @@ -1301,16 +1330,24 @@ amdgpu_userq_wait_for_signal(struct amdgpu_userq_mgr *uq_mgr)
>  	int ret;
>  
>  	xa_for_each(&uq_mgr->userq_xa, queue_id, queue) {
> +		queue = amdgpu_userq_get(uq_mgr, queue_id);
> +		if (!queue)
> +			continue;
> +
>  		struct dma_fence *f = queue->last_fence;
>  
> -		if (!f || dma_fence_is_signaled(f))
> +		if (!f || dma_fence_is_signaled(f)) {
> +			amdgpu_userq_put(uq_mgr, queue_id);
>  			continue;
> +		}
>  		ret = dma_fence_wait_timeout(f, true, msecs_to_jiffies(100));
>  		if (ret <= 0) {
>  			drm_file_err(uq_mgr->file, "Timed out waiting for fence=%llu:%llu\n",
>  				     f->context, f->seqno);
> +			amdgpu_userq_put(uq_mgr, queue_id);
>  			return -ETIMEDOUT;
>  		}
> +		amdgpu_userq_put(uq_mgr, queue_id);
>  	}
>  
>  	return 0;
> @@ -1368,9 +1405,15 @@ void amdgpu_userq_mgr_fini(struct amdgpu_userq_mgr *userq_mgr)
>  	mutex_lock(&userq_mgr->userq_mutex);
>  	amdgpu_userq_detect_and_reset_queues(userq_mgr);
>  	xa_for_each(&userq_mgr->userq_xa, queue_id, queue) {
> +		queue = amdgpu_userq_get(userq_mgr, queue_id);
> +		if (!queue)
> +			continue;
>  		amdgpu_userq_wait_for_last_fence(queue);
>  		amdgpu_userq_unmap_helper(queue);
>  		amdgpu_userq_cleanup(queue, queue_id);
> +		amdgpu_userq_put(userq_mgr, queue_id);
> +		/* Second put is for the reference taken in this function itself */
> +		amdgpu_userq_put(userq_mgr, queue_id);
>  	}
>  
>  	xa_destroy(&userq_mgr->userq_xa);
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.h
> index f4d1d46ae15e..ec3ce485626d 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.h
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.h
> @@ -74,6 +74,7 @@ struct amdgpu_usermode_queue {
>  	struct dentry		*debugfs_queue;
>  	struct delayed_work hang_detect_work;
>  	struct dma_fence *hang_detect_fence;
> +	struct kref		refcount;
>  
>  	struct list_head	userq_va_list;
>  };
> @@ -114,6 +115,9 @@ struct amdgpu_db_info {
>  	struct amdgpu_userq_obj	*db_obj;
>  };
>  
> +struct amdgpu_usermode_queue *amdgpu_userq_get(struct amdgpu_userq_mgr *uq_mgr, u32 qid);
> +void amdgpu_userq_put(struct amdgpu_userq_mgr *uq_mgr, u32 qid);
> +
>  int amdgpu_userq_ioctl(struct drm_device *dev, void *data, struct drm_file *filp);
>  
>  int amdgpu_userq_mgr_init(struct amdgpu_userq_mgr *userq_mgr, struct drm_file *file_priv,
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_userq_fence.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_userq_fence.c
> index 3c30512a6266..ba453361d2b4 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_userq_fence.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_userq_fence.c
> @@ -521,7 +521,7 @@ int amdgpu_userq_signal_ioctl(struct drm_device *dev, void *data,
>  		goto put_gobj_read;
>  
>  	/* Retrieve the user queue */
> -	queue = xa_load(&userq_mgr->userq_xa, args->queue_id);
> +	queue = amdgpu_userq_get(userq_mgr, args->queue_id);
>  	if (!queue) {
>  		r = -ENOENT;
>  		goto put_gobj_write;
> @@ -612,6 +612,9 @@ int amdgpu_userq_signal_ioctl(struct drm_device *dev, void *data,
>  free_syncobj_handles:
>  	kfree(syncobj_handles);
>  
> +	if (queue)
> +		amdgpu_userq_put(userq_mgr, args->queue_id);
> +
>  	return r;
>  }
>  
> @@ -863,7 +866,7 @@ int amdgpu_userq_wait_ioctl(struct drm_device *dev, void *data,
>  		 */
>  		num_fences = dma_fence_dedup_array(fences, num_fences);
>  
> -		waitq = xa_load(&userq_mgr->userq_xa, wait_info->waitq_id);
> +		waitq = amdgpu_userq_get(userq_mgr, wait_info->waitq_id);
>  		if (!waitq) {
>  			r = -EINVAL;
>  			goto free_fences;
> @@ -947,5 +950,8 @@ int amdgpu_userq_wait_ioctl(struct drm_device *dev, void *data,
>  free_syncobj_handles:
>  	kfree(syncobj_handles);
>  
> +	if (waitq)
> +		amdgpu_userq_put(userq_mgr, wait_info->waitq_id);
> +
>  	return r;
>  }