On Fri, Jun 19, 2020 at 05:23:18PM +0206, John Ogness wrote:

The reverse-order double lock dance in ioc_release_fn() is using a
retry loop. This is a problem on PREEMPT_RT because it could preempt
the task that would release q->queue_lock and thus live lock in the
retry loop.

RCU is already managing the freeing of the request queue and icq. If
the trylock fails, use RCU to guarantee that the request queue and
icq are not freed and re-acquire the locks in the correct order,
allowing forward progress.

Signed-off-by: John Ogness <john.ogness@linutronix.de>

Again, after starring on it for while and reading up and down,
I'd say, it looks good. Also a quick test run with blktests and
lockdep enabled didn't produce any warnings.

Reviewed-by: Daniel Wagner <redacted>