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

[Christoph Hellwig <hch@lst.de>]

On Thu, Sep 16, 2021 at 09:36:23AM +0800, Ming Lei wrote:
> >From correctness viewpoint, we need to call blk_cleanup_queue
> before releasing gendisk and after del_gendisk(). Now you have invented
> blk_cleanup_disk(), do you plan to do the three in one helper? :-)

No.  In retrospective blk_cleanup_disk wan't the best idea for a few
reasons.  But at least it consolidated some of the code.

> We don't have to put del_gendisk & blk_cleanup_queue together,

I don't want all of it together.  The important thing is that we have
two different concepts:

 - the gendisk is required to do file system style I/O
 - a standalone request_queue can be used for passthrough I/O.

> 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.

To take SCSI as the example.  We can unload the sd/sr drivers and the
queue needs to still be around and work for use with the sg driver.

> BTW, you asked the reproducer of the issue, I just observed the issue
> one or two time when running blktests block/009, but my scsi lifetime
> bpftrace script does show that gendisk is released before blk_cleanup_queue().

Interesting.  What were the symptoms in this case?