UPSTREAM: kernel: stop masking signals in create_io_thread()

[ Upstream commit b16b3855 ]

This is racy - move the blocking into when the task is created and
we're marking it as PF_IO_WORKER anyway. The IO threads are now
prepared to handle signals like SIGSTOP as well, so clear that from
the mask to allow proper stopping of IO threads.

Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Reported-by: Oleg Nesterov <oleg@redhat.com>
Change-Id: I6317c88e0723c6c97555f8ceacfee3692372ac4c
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 9ded44b6)
Bug: 268174392
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>