rust_binder: call set_notification_done() without proc lock

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

rust_binder: call set_notification_done() without proc lock

Consider the following sequence of events on a death listener:

1. The remote process dies and sends a BR_DEAD_BINDER message.

2. The local process invokes the BC_CLEAR_DEATH_NOTIFICATION command.

3. The local process then invokes the BC_DEAD_BINDER_DONE.

Then, the kernel will reply to the BC_DEAD_BINDER_DONE command with a

BR_CLEAR_DEATH_NOTIFICATION_DONE reply using push_work_if_looper().

However, this can result in a deadlock if the current thread is not a

looper. This is because dead_binder_done() still holds the proc lock

during set_notification_done(), which called push_work_if_looper().

Normally, push_work_if_looper() takes the thread lock, which is fine to

take under the proc lock. But if the current thread is not a looper,

then it falls back to delivering the reply to the process work queue,

which involves taking the proc lock. Since the proc lock is already

held, this is a deadlock.

Fix this by releasing the proc lock during set_notification_done(). It

was not intentional that it was held during that function to begin with.

I don't think this ever happens in Android because BC_DEAD_BINDER_DONE

is only invoked in response to BR_DEAD_BINDER messages, and the kernel

always delivers BR_DEAD_BINDER to a looper. So there's no scenario where

Android userspace will call BC_DEAD_BINDER_DONE on a non-looper thread.