Re: [PATCH] blk-mq: quiesce queue while reallocating hctxs

[Yu Kuai]

Hi,

在 2023/03/03 9:24, Keith Busch 写道:
> On Tue, Feb 21, 2023 at 05:24:36PM +0800, Yu Kuai wrote:
> > From: Yu Kuai <yukuai3@xxxxxxxxxx>
> >
> > commit 8237c01f1696 ("blk-mq: use quiesced elevator switch when
> > reinitializing queues") add quiesce queue while switching elevator,
> > however, if old elevator is none, queue is still not quiesced. Hence
> > reallocating hctxs can concurrent with run queue. Fix it by also
> > quiesce queue in the beginning of __blk_mq_update_nr_hw_queues().
>
> Is this actually fixing anything? The quiesced elevator switch was to prevent
> use-after-free from an elevator being torn down, but if you are not switching
> elevators, then what resource does quiescing protect?
> .

What I can think of is hctx itself. run queue can fetch a hctx that will
be exited, I did't found any real problems yet, but I don't think it
is not good to run work for a exited or reused hctx.

Thanks,
Kuai