diff --git a/scst/src/dev_handlers/kunit/vdisk/suites/scst_vdisk_sync_test.c b/scst/src/dev_handlers/kunit/vdisk/suites/scst_vdisk_sync_test.c
index a24eca388..2793dd67c 100644
--- a/scst/src/dev_handlers/kunit/vdisk/suites/scst_vdisk_sync_test.c
+++ b/scst/src/dev_handlers/kunit/vdisk/suites/scst_vdisk_sync_test.c
@@ -205,12 +205,6 @@ static void vdisk_backend_test(struct kunit *test)
 	struct vdisk_test_fixture *f = test->priv;
 	int ret;
 
-	/* Avoid dereferencing a closed backend until its lifetime is fixed. */
-	if (p->closed && !p->nullio) {
-		kunit_skip(test, "closed-backend sync needs a separate lifetime fix");
-		return;
-	}
-
 	f->vdev.dev_active = !p->inactive;
 	f->vdev.nullio = p->nullio;
 	f->vdev.blockio = p->blockio;
@@ -221,9 +215,9 @@ static void vdisk_backend_test(struct kunit *test)
 	f->block_flush_result = p->error;
 	f->sysfs_sync = true;
 
-	/* Exercise the existing store callback with an unregistered private device. */
-	ret = vdisk_sysfs_sync_store(&f->dev.dev_kobj, NULL, "1", 1);
-	KUNIT_EXPECT_EQ(test, ret, p->expected ? p->expected : 1);
+	/* Keep task-scoped backend stubs in the test thread on this private device. */
+	ret = vdisk_flush_backend(&f->dev);
+	KUNIT_EXPECT_EQ(test, ret, p->expected);
 	/* Empty files may still need metadata synchronization. */
 	if (!p->empty)
 		KUNIT_EXPECT_EQ(test, f->flush_count, p->files);
diff --git a/scst/src/dev_handlers/scst_vdisk_main.c b/scst/src/dev_handlers/scst_vdisk_main.c
index 3d7007c75..da454d624 100644
--- a/scst/src/dev_handlers/scst_vdisk_main.c
+++ b/scst/src/dev_handlers/scst_vdisk_main.c
@@ -7492,24 +7492,72 @@ out_e_unlock:
 	goto out_resume;
 }
 
+/*
+ * For a live device, the caller must suspend activity and hold scst_mutex
+ * and the ALUA lock to prevent the backend from being closed or reopened.
+ */
 SCST_KUNIT_VISIBLE
-ssize_t vdisk_sysfs_sync_store(struct kobject *kobj, struct kobj_attribute *attr,
-			       const char *buf, size_t count)
+int vdisk_flush_backend(struct scst_device *dev)
 {
-	struct scst_device *dev =
-		container_of(kobj, struct scst_device, dev_kobj);
 	struct scst_vdisk_dev *virt_dev = dev->dh_priv;
+
+	/* Queued work can outlive removal of the handler's sysfs files. */
+	if (!virt_dev)
+		return -ENODEV;
+	if (virt_dev->nullio)
+		return 0;
+	if (!vdisk_is_open(virt_dev))
+		return -ENOMEDIUM;
+	if (virt_dev->blockio)
+		return vdisk_blockio_flush(virt_dev->bdev_desc.bdev, GFP_KERNEL, false,
+					   NULL, false);
+
+	return __vdisk_fsync_fileio(0, i_size_read(file_inode(virt_dev->fd)),
+				    dev, NULL, virt_dev->fd);
+}
+
+static int vdisk_sysfs_process_sync_store(struct scst_sysfs_work_item *work)
+{
+	struct scst_device *dev = work->dev;
 	int res;
 
-	if (virt_dev->nullio)
-		res = 0;
-	else if (virt_dev->blockio)
-		res = vdisk_blockio_flush(virt_dev->bdev_desc.bdev, GFP_KERNEL, false, NULL,
-					  false);
-	else
-		res = __vdisk_fsync_fileio(0, i_size_read(file_inode(virt_dev->fd)),
-					   dev, NULL, virt_dev->fd);
+	/* MODE SELECT and task management can also reopen the backing file. */
+	res = scst_suspend_activity(SCST_SUSPEND_TIMEOUT_USER);
+	if (res)
+		goto out;
 
+	res = mutex_lock_interruptible(&scst_mutex);
+	if (res)
+		goto resume;
+
+	/* Serialize with target detach, activation and ALUA state changes. */
+	scst_alua_lock();
+	res = vdisk_flush_backend(dev);
+	scst_alua_unlock();
+	mutex_unlock(&scst_mutex);
+resume:
+	scst_resume_activity();
+out:
+	kobject_put(&dev->dev_kobj);
+	return res;
+}
+
+static ssize_t vdisk_sysfs_sync_store(struct kobject *kobj, struct kobj_attribute *attr,
+				      const char *buf, size_t count)
+{
+	struct scst_device *dev = container_of(kobj, struct scst_device, dev_kobj);
+	struct scst_sysfs_work_item *work;
+	int res;
+
+	res = scst_alloc_sysfs_work(vdisk_sysfs_process_sync_store, false, &work);
+	if (res)
+		return res;
+
+	work->dev = dev;
+	SCST_SET_DEP_MAP(work, &scst_dev_dep_map);
+	kobject_get(&dev->dev_kobj);
+
+	res = scst_sysfs_queue_wait_work(work);
 	return res ? : count;
 }
 
diff --git a/scst/src/dev_handlers/scst_vdisk_test.h b/scst/src/dev_handlers/scst_vdisk_test.h
index d4327c605..902e07fe1 100644
--- a/scst/src/dev_handlers/scst_vdisk_test.h
+++ b/scst/src/dev_handlers/scst_vdisk_test.h
@@ -19,8 +19,7 @@ void vdisk_on_free_cmd_params(const struct vdisk_cmd_params *p);
 enum compl_status_e vdisk_exec_sai_16(struct vdisk_cmd_params *p);
 enum compl_status_e fileio_exec_write(struct vdisk_cmd_params *p);
 enum compl_status_e fileio_exec_read(struct vdisk_cmd_params *p);
-ssize_t vdisk_sysfs_sync_store(struct kobject *kobj, struct kobj_attribute *attr,
-			       const char *buf, size_t count);
+int vdisk_flush_backend(struct scst_device *dev);
 
 #endif /* SCST_KUNIT_ENABLED */
 #endif /* SCST_VDISK_TEST_H */