Comment 2 for bug 1558447

Reproduced this on a vivid VM. All of the failing processes are hanging sending data to a unix domain socket.

Tracked this down to a bad backport applied to the kernel:

  commit 5981b6969d649a4fe1d402c915eb751c1243410c
  Author: Joseph Salisbury <email address hidden>
  Date: Fri Mar 4 14:33:47 2016 -0500

    Revert "af_unix: Revert 'lock_interruptible' in stream receive code"

This is missing a removal of a mutex_lock() in the second stanza. Looking at what was reviewed and acked this was present in that version. Possibly this was damaged in application due to the presence of the commit below:

  commit 0c0b98c6005644d1d00c8b91fbb0cea0032f99b2
  Author: Rainer Weikusat <email address hidden>
  Date: Mon Feb 8 18:47:19 2016 +0000

    af_unix: Don't set err in unix_stream_read_generic unless there was an error

Which appears to actually be the proper fix for the issue the revert is attempting to fix.