[BUG] android: possible ABBA deadlock in print_binder_proc() and binder_get_txn_from_and_acq_inner()

[Jia-Ju Bai]

Hello,

My static analysis tool reports a possible ABBA deadlock in the android 
driver in Linux 5.10:

print_binder_proc()
  binder_inner_proc_lock()
    _binder_inner_proc_lock()
      spin_lock(&proc->inner_lock); --> Line 662 (Lock A)
  print_binder_thread_ilocked()
    print_binder_transaction_ilocked()
      spin_lock(&t->lock); --> Line 5531 (Lock B)

binder_get_txn_from_and_acq_inner()
  binder_get_txn_from()
    spin_lock(&t->lock); --> Line 1833 (Lock B)
  binder_inner_proc_lock()
    _binder_inner_proc_lock()
      spin_lock(&proc->inner_lock); --> Line 662 (Lock A)

When print_binder_proc() and binder_get_txn_from_and_acq_inner() are 
concurrently executed, the deadlock can occur.

I am not quite sure whether this possible deadlock is real and how to 
fix it if it is real.
Any feedback would be appreciated, thanks :)

Reported-by: TOTE Robot <oslab@xxxxxxxxxxxxxxx>


Best wishes,
Jia-Ju Bai