Re: tear down file system I/O in del_gendisk v3

This patchset fixed the NULL pointer issue triggered by blktests block/025
https://lore.kernel.org/linux-block/YWfJ06KX3HT1nANX@infradead.org/T/#mbf26cd34c88660ce0221dd7933b294a0b0298319 (local)

Tested-by: Yi Zhang <redacted>

On Wed, Sep 29, 2021 at 3:14 PM Christoph Hellwig [off-list ref] wrote:

Ming reported that for SCSI we have a lifetime problem now that
the BDI moved from the request_queue to the disk as del_gendisk
doesn't finish all outstanding file system I/O.  It turns out
this actually is an older problem, although the case where it could
be hit before was very unusual (unbinding of a SCSI upper driver
while the scsi_device stays around).  This series fixes this by
draining all I/O in del_gendisk.

Changes since v2:
 - move the call to submit_bio_checks into freeze protection

Changes since v1:
 - fix a commit log typo
 - keep the existing nowait vs queue dying semantics in bio_queue_enter
 - actually keep q_usage_counter in atomic mode after del_gendisk

-- 
Best Regards,
  Yi Zhang