Description of problem:
If a fuse filesystem is mounted inside a container, there is a problem
during pid namespace destruction. The scenario is:

1. task (a thread in the fuse server, with a fuse file open) starts
   exiting, does exit_signals(), goes into fuse_flush() -> wait
2. fuse daemon gets killed, tries to wake everyone up
3. task from 1 is stuck because complete_signal() doesn't wake it up, since
   it has PF_EXITING.

The result is that the thread will never be woken up, and pid namespace
destruction will block indefinitely.

To add insult to injury, nobody is waiting for these return codes, since
the pid namespace is being destroyed.


Version-Release number of selected component (if applicable):


How reproducible:


Steps to Reproduce:
1.
2.
3.

Actual results:


Expected results:


Additional info: