Pull io_uring fixes from Jens Axboe:

 - A tweak to IOSQE_IO_LINK (also marked for stable) to allow links that
   don't sever if the result is < 0.

   This is mostly for linked timeouts, where if we ask for a pure
   timeout we always get -ETIME. This makes links useless for that case,
   hence allow a case where it works.

 - Five minor optimizations to fix and improve cases that regressed
   since v5.4.

 - An SQTHREAD locking fix.

 - A sendmsg/recvmsg iov assignment fix.

 - Net fix where read_iter/write_iter don't honor IOCB_NOWAIT, and
   subsequently ensuring that works for io_uring.

 - Fix a case where for an invalid opcode we might return -EBADF instead
   of -EINVAL, if the ->fd of that sqe was set to an invalid fd value.

* tag 'io_uring-5.5-20191212' of git://git.kernel.dk/linux-block:
  io_uring: ensure we return -EINVAL on unknown opcode
  io_uring: add sockets to list of files that support non-blocking issue
  net: make socket read/write_iter() honor IOCB_NOWAIT
  io_uring: only hash regular files for async work execution
  io_uring: run next sqe inline if possible
  io_uring: don't dynamically allocate poll data
  io_uring: deferred send/recvmsg should assign iov
  io_uring: sqthread should grab ctx->uring_lock for submissions
  io-wq: briefly spin for new work after finishing work
  io-wq: remove worker->wait waitqueue
  io_uring: allow unbreakable links