driver core: fix deadlock in __device_attach

In the Linux kernel, the following vulnerability has been resolved:

driver core: fix deadlock in __device_attach

In __device_attach function, The lock holding logic is as follows:

...

__device_attach

device_lock(dev) // get lock dev

async_schedule_dev(__device_attach_async_helper, dev); // func

async_schedule_node

async_schedule_node_domain(func)

entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC);

/* when fail or work limit, sync to execute func, but

__device_attach_async_helper will get lock dev as

well, which will lead to A-A deadlock. */

if (!entry || atomic_read(&entry_count) > MAX_WORK) {

func;

else

queue_work_node(node, system_unbound_wq, &entry->work)

device_unlock(dev)

As shown above, when it is allowed to do async probes, because of

out of memory or work limit, async work is not allowed, to do

sync execute instead. it will lead to A-A deadlock because of

__device_attach_async_helper getting lock dev.

To fix the deadlock, move the async_schedule_dev outside device_lock,

as we can see, in async_schedule_node_domain, the parameter of

queue_work_node is system_unbound_wq, so it can accept concurrent

operations. which will also not change the code logic, and will

not lead to deadlock.