UPSTREAM: kernel: don't call do_exit() for PF_IO_WORKER threads

[ Upstream commit 10442994 ]

Right now we're never calling get_signal() from PF_IO_WORKER threads, but
in preparation for doing so, don't handle a fatal signal for them. The
workers have state they need to cleanup when exiting, so just return
instead of calling do_exit() on their behalf. The threads themselves will
detect a fatal signal and do proper shutdown.

Change-Id: Iedc3fae8cb496d003852c87fdefacc1ad7601cc5
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 831cb78a)
Bug: 268174392
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>