drm/panthor: Lock the VM resv before calling drm_gpuvm_bo_obtain_prealloc()

drm_gpuvm_bo_obtain_prealloc() will call drm_gpuvm_bo_put() on our
pre-allocated BO if the <BO,VM> association exists. Given we
only have one ref on preallocated_vm_bo, drm_gpuvm_bo_destroy() will
be called immediately, and we have to hold the VM resv lock when
calling this function.

Fixes: 647810ec2476 ("drm/panthor: Add the MMU/VM logical block")
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240913112722.492144-1-boris.brezillon@collabora.com

diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
index bbc12728437f1365472b7f572f3d21fefcdd337e..3cd2bce59edcd70aa8dc8e059ed043e28a781525 100644 (file)
--- a/drivers/gpu/drm/panthor/panthor_mmu.c
+++ b/drivers/gpu/drm/panthor/panthor_mmu.c
@@ -1251,9 +1251,17 @@ static int panthor_vm_prepare_map_op_ctx(struct panthor_vm_op_ctx *op_ctx,
                goto err_cleanup;
        }
 
+       /* drm_gpuvm_bo_obtain_prealloc() will call drm_gpuvm_bo_put() on our
+        * pre-allocated BO if the <BO,VM> association exists. Given we
+        * only have one ref on preallocated_vm_bo, drm_gpuvm_bo_destroy() will
+        * be called immediately, and we have to hold the VM resv lock when
+        * calling this function.
+        */
+       dma_resv_lock(panthor_vm_resv(vm), NULL);
        mutex_lock(&bo->gpuva_list_lock);
        op_ctx->map.vm_bo = drm_gpuvm_bo_obtain_prealloc(preallocated_vm_bo);
        mutex_unlock(&bo->gpuva_list_lock);
+       dma_resv_unlock(panthor_vm_resv(vm));
 
        /* If the a vm_bo for this <VM,BO> combination exists, it already
         * retains a pin ref, and we can release the one we took earlier.