UPSTREAM: kernel: provide create_io_thread() helper

[ Upstream commit cc440e87 ]

Provide a generic helper for setting up an io_uring worker. Returns a
task_struct so that the caller can do whatever setup is needed, then call
wake_up_new_task() to kick it into gear.

Add a kernel_clone_args member, io_thread, which tells copy_process() to
mark the task with PF_IO_WORKER.

Change-Id: I670f155fc4ac1b93824391292f4822e32671215b
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 1500fed0)
Bug: 268174392
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>