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

[Rainer Weikusat <rweikusat@mobileactivedefense.com>]

Rainer Weikusat <rw@doppelsaurus.mobileactivedefense.com> 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).