Based on the provided code snippet and the identified CWE-457  vulnerability at line 7, here are five possible patches to address the issue:

Patch 1: Add a null check before unlocking the mutex
```
7 	if (spi && spi->controller)
8 		mutex_unlock(&spi->controller->bus_lock_mutex);
```

Patch 2: Use a local variable to store the mutex reference
```
3 	int ret;
4 	struct mutex *bus_lock_mutex = &spi->controller->bus_lock_mutex;
5 
6 	mutex_lock(bus_lock_mutex);
7 	ret = __spi_sync(spi, message);
8 	mutex_unlock(bus_lock_mutex);
```

Patch 3: Refactor to use a lock/unlock wrapper function
```
1 int spi_sync(struct spi_device *spi, struct spi_message *message)
2 {
3 	int ret;
4 
5 	ret = spi_sync_locked(spi, message);
6 
7 	return ret;
8 }
9 
10 static int spi_sync_locked(struct spi_device *spi, struct spi_message *message)
11 {
12 	int ret;
13 
14 	mutex_lock(&spi->controller->bus_lock_mutex);
15 	ret = __spi_sync(spi, message);
16 	mutex_unlock(&spi->controller->bus_lock_mutex);
17 
18 	return ret;
19 }
```

Patch 4: Use a reference-counted locking mechanism
```
1 int spi_sync(struct spi_device *spi, struct spi_message *message)
2 {
3 	int ret;
4 
5 	if (!spi_bus_get(spi->controller))
6 		return -ENODEV;
7 	
8 	mutex_lock(&spi->controller->bus_lock_mutex);
9 	ret = __spi_sync(spi, message);
10 	mutex_unlock(&spi->controller->bus_lock_mutex);
11 	
12 	spi_bus_put(spi->controller);
13 
14 	return ret;
15 }
```

Patch 5: Use a trylock mechanism with error handling
```
1 int spi_sync(struct spi_device *spi, struct spi_message *message)
2 {
3 	int ret;
4 
5 	if (!mutex_trylock(&spi->controller->bus_lock_mutex))
6 		return -EBUSY;
7 	
8 	ret = __spi_sync(spi, message);
9 	
10 	if (spi && spi->controller)
11 		mutex_unlock(&spi->controller->bus_lock_mutex);
12 
13 	return ret;
14 }
```

These patches aim to prevent the use-after-free vulnerability by ensuring proper handling of the mutex and the spi controller reference.