Re: [PATCH v2] md: do not _put wrong device in md_seq_next

[Mariusz Tkaczyk <mariusz.tkaczyk@linux.intel.com>]

On Tue, 12 Sep 2023 21:25:24 +0800
Yu Kuai <yukuai1@huaweicloud.com> wrote:

> Hi,
> 
> 在 2023/09/12 21:01, Mariusz Tkaczyk 写道:
> > During working on changes proposed by Kuai [1], I determined that
> > mddev->active is continusly decremented for array marked by MD_CLOSING.
> > It brought me to md_seq_next() changed by [2]. I determined the regression
> > here, if mddev_get() fails we updated mddev pointer and as a result we
> > _put failed device.  
> 
> This mddev is decremented while there is another mddev increased, that's
> why AceLan said that single array can't reporduce the problem.
> 
> And because mddev->active is leaked, then del_gendisk() will never be
> called for the mddev while closing the array, that's why user will
> always see this array, cause infiniate loop open -> stop array -> close
> for systemd-shutdown.

Ohh, I see the scenario now...
First array can be successfully stopped. We marked MD_DELETED and proceed
with scheduling wq but in the middle of that md_seq_next() increased active for
other array and decrement active for the one with MD_DELETED.
For this next array we are unable to reach active == 0 anymore.

Song, let me know if you need description like that in commit message.

Thanks!
Mariusz