Re: [V4.4-rc6 Regression] af_unix: Revert 'lock_interruptible' in stream receive code

Rainer Weikusat [off-list ref] writes:

[...]

The start uses that to record an error which might need to be
reported, the return statement uses it to indicate that an error has
occurred. Hence, some kind of in-between translation must occur.  The
mutex_lock_interruptible happened to do that but that was never it's
intended purpose.

Additional information: The 'trick' of using recvmsg w/o a receive
buffer in order to retrieve control messages in fact wouldn't have
worked with the unix_stream_recvmsg prior to introduction of the
interruptible lock as that (judging from the git source) would have
triggered all the same issues,

	- -EOPNOTSUP if a msg was available

        - -EAGAIN if the code had to wait

        - not receiving the creds if the -EAGAIN hadn't happened because
          of the continue (that's the other patch)

IOW, that's a feature inadvertendly added by an otherwise useless code
change (mea culpa).