Comment 23 for bug 1540731

This is the commit that introduced this regression in V4.4-rc6:

commit 3822b5c2fc62e3de8a0f33806ff279fb7df92432
Author: Rainer Weikusat <email address hidden>
Date: Wed Dec 16 20:09:25 2015 +0000

    af_unix: Revert 'lock_interruptible' in stream receive code

    With b3ca9b02b00704053a38bfe4c31dbbb9c13595d0, the AF_UNIX SOCK_STREAM
    receive code was changed from using mutex_lock(&u->readlock) to
    mutex_lock_interruptible(&u->readlock) to prevent signals from being
    delayed for an indefinite time if a thread sleeping on the mutex
    happened to be selected for handling the signal. But this was never a
    problem with the stream receive code (as opposed to its datagram
    counterpart) as that never went to sleep waiting for new messages with the
    mutex held and thus, wouldn't cause secondary readers to block on the
    mutex waiting for the sleeping primary reader. As the interruptible
    locking makes the code more complicated in exchange for no benefit,
    change it back to using mutex_lock.

    Signed-off-by: Rainer Weikusat <email address hidden>
    Acked-by: Hannes Frederic Sowa <email address hidden>
    Signed-off-by: David S. Miller <email address hidden>