Re: [PATCH] scsi: core: cleanup request queue before releasing gendisk

[Christoph Hellwig <hch@lst.de>]

On Thu, Sep 16, 2021 at 08:38:16PM +0800, Ming Lei wrote:
> > > and it may cause other trouble at least for scsi disk since sd_shutdown()
> > > follows del_gendisk() and has to be called before blk_cleanup_queue().
> > 
> > Yes.  So we need to move the bits of blk_cleanup_queue that deal with
> > the file system I/O state to del_gendisk, and keep blk_cleanup_queue
> > for anything actually needed for the low-level queue.
> 
> Can you explain what the bits are in blk_cleanup_queue() for dealing with FS
> I/O state? blk_cleanup_queue() drains and shutdown the queue basically,
> all shouldn't be related with gendisk, and it is fine to implement one
> queue without gendisk involved, such as nvme admin, connect queue or
> sort of stuff.
> 
> Wrt. this reported issue, rq_qos_exit() needs to run before releasing
> gendisk, but queue has to put into freezing before calling
> rq_qos_exit(),

I was curious what you hit, but yes rq_qos_exit is obvious.
blk_flush_integrity also is very much about fs I/O state.



> so looks you suggest to move the following code into
> del_gendisk()?

something like that.  I think we need to split the dying flag into
one for the gendisk and one for the queue first, and make sure the
queue freeze in del_gendisk is released again so that passthrough
still works after.

> If we move the above into del_gendisk(), some corner cases have to be
> taken care of, such as request queue without disk involved.

Yes.