On Thu, May 20, 2021 at 5:57 PM Ming Lei <ming.lei@redhat.com> wrote:
>
> On Fri, May 21, 2021 at 12:33:53AM +0200, Jan Kara wrote:
> > Lockdep complains about lock inversion between ioc->lock and bfqd->lock:
> >
> > bfqd -> ioc:
> >  put_io_context+0x33/0x90 -> ioc->lock grabbed
> >  blk_mq_free_request+0x51/0x140
> >  blk_put_request+0xe/0x10
> >  blk_attempt_req_merge+0x1d/0x30
> >  elv_attempt_insert_merge+0x56/0xa0
> >  blk_mq_sched_try_insert_merge+0x4b/0x60
> >  bfq_insert_requests+0x9e/0x18c0 -> bfqd->lock grabbed
>
> We could move blk_put_request() into scheduler code, then the lock
> inversion is avoided. So far only mq-deadline and bfq calls into
> blk_mq_sched_try_insert_merge(), and this change should be small.

We'd potentially be putting multiple requests if we keep the recursive merge.

Could we move backmerge loop to the schedulers, perhaps?

>
>
> Thanks,
> Ming
>