block: null_blk: Fix handling of fake timeout request

block: null_blk: Fix handling of fake timeout request

When injecting a fake timeout into the null_blk driver using
fail_io_timeout, the request timeout handler does not execute
blk_mq_complete_request(), so the complete callback is never executed
for a timedout request.

The null_blk driver also has a driver-specific fake timeout mechanism
which does not have this problem. Fix the problem with fail_io_timeout
by using the same meachanism as null_blk internal timeout feature, using
the fake_timeout field of null_blk commands.

Reported-by: Akinobu Mita <akinobu.mita@gmail.com>
Fixes: de3510e52b0a ("null_blk: fix command timeout completion handling")
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Link: https://lore.kernel.org/r/20230314041106.19173-2-damien.lemoal@opensource.wdc.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>