drm/sa: Split drm_suballoc_new() into SA alloc and init helpers

drm_suballoc_new() currently both allocates the SA object using kmalloc()
and searches for a suitable hole in the sub-allocator for the requested
size. If SA allocation is done by holding sub-allocator mutex, this design
can lead to reclaim safety issues.

By splitting the kmalloc() step outside of the critical section, we allow
the memory allocation to use GFP_KERNEL (reclaim-safe) while ensuring that
the initialization step that holds reclaim-tainted locks (sub-allocator
mutex) operates in a reclaim-unsafe context with pre-allocated memory.

This separation prevents potential deadlocks where memory reclaim could
attempt to acquire locks that are already held during the sub-allocator
operations.

Signed-off-by: Satyanarayana K V P <satyanarayana.k.v.p@intel.com>
Suggested-by: Matthew Brost <matthew.brost@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: dri-devel@lists.freedesktop.org
Cc: Maarten Lankhorst <dev@lankhorst.se>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Acked-by: Maarten Lankhorst <dev@lankhorst.se>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20260220055519.2485681-6-satyanarayana.k.v.p@intel.com

drivers/gpu/drm/drm_suballoc.c

@@ -293,45 +293,66 @@ static bool drm_suballoc_next_hole(struct drm_suballoc_manager *sa_manager,
 }
 
 /**
- * drm_suballoc_new() - Make a suballocation.
+ * drm_suballoc_alloc() - Allocate uninitialized suballoc object.
+ * @gfp: gfp flags used for memory allocation.
+ *
+ * Allocate memory for an uninitialized suballoc object. Intended usage is
+ * allocate memory for suballoc object outside of a reclaim tainted context
+ * and then be initialized at a later time in a reclaim tainted context.
+ *
+ * @drm_suballoc_free() should be used to release the memory if returned
+ * suballoc object is in uninitialized state.
+ *
+ * Return: a new uninitialized suballoc object, or an ERR_PTR(-ENOMEM).
+ */
+struct drm_suballoc *drm_suballoc_alloc(gfp_t gfp)
+{
+	struct drm_suballoc *sa;
+
+	sa = kmalloc(sizeof(*sa), gfp);
+	if (!sa)
+		return ERR_PTR(-ENOMEM);
+
+	sa->manager = NULL;
+
+	return sa;
+}
+EXPORT_SYMBOL(drm_suballoc_alloc);
+
+/**
+ * drm_suballoc_insert() - Initialize a suballocation and insert a hole.
  * @sa_manager: pointer to the sa_manager
+ * @sa: The struct drm_suballoc.
  * @size: number of bytes we want to suballocate.
- * @gfp: gfp flags used for memory allocation. Typically GFP_KERNEL but
- *       the argument is provided for suballocations from reclaim context or
- *       where the caller wants to avoid pipelining rather than wait for
- *       reclaim.
  * @intr: Whether to perform waits interruptible. This should typically
  *        always be true, unless the caller needs to propagate a
  *        non-interruptible context from above layers.
  * @align: Alignment. Must not exceed the default manager alignment.
  *         If @align is zero, then the manager alignment is used.
  *
- * Try to make a suballocation of size @size, which will be rounded
+ * Try to make a suballocation on a pre-allocated suballoc object of size @size,
- * up to the alignment specified in specified in drm_suballoc_manager_init().
+ * which will be rounded up to the alignment specified in specified in
+ * drm_suballoc_manager_init().
  *
- * Return: a new suballocated bo, or an ERR_PTR.
+ * Return: zero on success, errno on failure.
  */
-struct drm_suballoc *
+int drm_suballoc_insert(struct drm_suballoc_manager *sa_manager,
-drm_suballoc_new(struct drm_suballoc_manager *sa_manager, size_t size,
+			struct drm_suballoc *sa, size_t size,
-		 gfp_t gfp, bool intr, size_t align)
+			bool intr, size_t align)
 {
 	struct dma_fence *fences[DRM_SUBALLOC_MAX_QUEUES];
 	unsigned int tries[DRM_SUBALLOC_MAX_QUEUES];
 	unsigned int count;
 	int i, r;
-	struct drm_suballoc *sa;
 
 	if (WARN_ON_ONCE(align > sa_manager->align))
-		return ERR_PTR(-EINVAL);
+		return -EINVAL;
 	if (WARN_ON_ONCE(size > sa_manager->size || !size))
-		return ERR_PTR(-EINVAL);
+		return -EINVAL;
 
 	if (!align)
 		align = sa_manager->align;
 
-	sa = kmalloc(sizeof(*sa), gfp);
-	if (!sa)
-		return ERR_PTR(-ENOMEM);
 	sa->manager = sa_manager;
 	sa->fence = NULL;
 	INIT_LIST_HEAD(&sa->olist);
@@ -348,7 +369,7 @@ drm_suballoc_new(struct drm_suballoc_manager *sa_manager, size_t size,
 			if (drm_suballoc_try_alloc(sa_manager, sa,
 						   size, align)) {
 				spin_unlock(&sa_manager->wq.lock);
-				return sa;
+				return 0;
 			}
 
 			/* see if we can skip over some allocations */
@@ -385,8 +406,48 @@ drm_suballoc_new(struct drm_suballoc_manager *sa_manager, size_t size,
 	} while (!r);
 
 	spin_unlock(&sa_manager->wq.lock);
-	kfree(sa);
+	sa->manager = NULL;
-	return ERR_PTR(r);
+	return r;
+}
+EXPORT_SYMBOL(drm_suballoc_insert);
+
+/**
+ * drm_suballoc_new() - Make a suballocation.
+ * @sa_manager: pointer to the sa_manager
+ * @size: number of bytes we want to suballocate.
+ * @gfp: gfp flags used for memory allocation. Typically GFP_KERNEL but
+ *       the argument is provided for suballocations from reclaim context or
+ *       where the caller wants to avoid pipelining rather than wait for
+ *       reclaim.
+ * @intr: Whether to perform waits interruptible. This should typically
+ *        always be true, unless the caller needs to propagate a
+ *        non-interruptible context from above layers.
+ * @align: Alignment. Must not exceed the default manager alignment.
+ *         If @align is zero, then the manager alignment is used.
+ *
+ * Try to make a suballocation of size @size, which will be rounded
+ * up to the alignment specified in specified in drm_suballoc_manager_init().
+ *
+ * Return: a new suballocated bo, or an ERR_PTR.
+ */
+struct drm_suballoc *
+drm_suballoc_new(struct drm_suballoc_manager *sa_manager, size_t size,
+		 gfp_t gfp, bool intr, size_t align)
+{
+	struct drm_suballoc *sa;
+	int err;
+
+	sa = drm_suballoc_alloc(gfp);
+	if (IS_ERR(sa))
+		return sa;
+
+	err = drm_suballoc_insert(sa_manager, sa, size, intr, align);
+	if (err) {
+		drm_suballoc_free(sa, NULL);
+		return ERR_PTR(err);
+	}
+
+	return sa;
 }
 EXPORT_SYMBOL(drm_suballoc_new);
 
@@ -405,6 +466,11 @@ void drm_suballoc_free(struct drm_suballoc *suballoc,
 	if (!suballoc)
 		return;
 
+	if (!suballoc->manager) {
+		kfree(suballoc);
+		return;
+	}
+
 	sa_manager = suballoc->manager;
 
 	spin_lock(&sa_manager->wq.lock);

include/drm/drm_suballoc.h

@@ -53,6 +53,12 @@ void drm_suballoc_manager_init(struct drm_suballoc_manager *sa_manager,
 
 void drm_suballoc_manager_fini(struct drm_suballoc_manager *sa_manager);
 
+struct drm_suballoc *drm_suballoc_alloc(gfp_t gfp);
+
+int drm_suballoc_insert(struct drm_suballoc_manager *sa_manager,
+			struct drm_suballoc *sa, size_t size, bool intr,
+			size_t align);
+
 struct drm_suballoc *
 drm_suballoc_new(struct drm_suballoc_manager *sa_manager, size_t size,
 		 gfp_t gfp, bool intr, size_t align);