[PATCH v3] drm/panthor: Fix potential memleak of vma structure

[Akash Goel <akash.goel@arm.com>]

This commit addresses a memleak issue of panthor_vma (or drm_gpuva)
structure in Panthor driver, that can happen if the GPU page table
update operation to map the pages fail.
The issue is very unlikely to occur in practice.

v2: Add panthor_vm_op_ctx_return_vma() helper (Boris)

v3: Add WARN_ON_ONCE (Boris)

Fixes: 647810ec2476 ("drm/panthor: Add the MMU/VM logical block")
Signed-off-by: Akash Goel <akash.goel@arm.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
---
 drivers/gpu/drm/panthor/panthor_mmu.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
index 6dec4354e378..56a53d70f3b2 100644
--- a/drivers/gpu/drm/panthor/panthor_mmu.c
+++ b/drivers/gpu/drm/panthor/panthor_mmu.c
@@ -1146,6 +1146,20 @@ static void panthor_vm_cleanup_op_ctx(struct panthor_vm_op_ctx *op_ctx,
 	}
 }
 
+static void
+panthor_vm_op_ctx_return_vma(struct panthor_vm_op_ctx *op_ctx,
+			     struct panthor_vma *vma)
+{
+	for (u32 i = 0; i < ARRAY_SIZE(op_ctx->preallocated_vmas); i++) {
+		if (!op_ctx->preallocated_vmas[i]) {
+			op_ctx->preallocated_vmas[i] = vma;
+			return;
+		}
+	}
+
+	WARN_ON_ONCE(1);
+}
+
 static struct panthor_vma *
 panthor_vm_op_ctx_get_vma(struct panthor_vm_op_ctx *op_ctx)
 {
@@ -2081,8 +2095,10 @@ static int panthor_gpuva_sm_step_map(struct drm_gpuva_op *op, void *priv)
 	ret = panthor_vm_map_pages(vm, op->map.va.addr, flags_to_prot(vma->flags),
 				   op_ctx->map.sgt, op->map.gem.offset,
 				   op->map.va.range);
-	if (ret)
+	if (ret) {
+		panthor_vm_op_ctx_return_vma(op_ctx, vma);
 		return ret;
+	}
 
 	/* Ref owned by the mapping now, clear the obj field so we don't release the
 	 * pinning/obj ref behind GPUVA's back.
-- 
2.25.1