[PATCH 0/4 v9] SCSI device removal fixes

[Bart Van Assche <bvanassche@acm.org>]

This is version nine of the SCSI device removal patch series. This
patch series has been tested by triggering a large number of removals of
a SCSI device controlled by the ib_srp LLD and at the same time running
an I/O integrity test with fio on a dm device on top of the SRP SCSI device.

Changes compared to v8:
- Replaced the block layer patch (1/4) by a more comprehensive patch
  from Muthukumar Ratty.
- Added "Reviewed-by: Mike Christie" in patches 2/4..4/4.

Changes compared to v7:
- Made sure that __scsi_queue_insert() processes the request that has
  been passed to that function. Added a comment in that function too.
- Fixed a typo in the description of the first patch in this series
  and removed "CC: stable".

Changes compared to v6:
- Added a fix for a race in the block layer.
- Moved a BUG_ON(!sdev) statement up since it's a precondition check.
- Changed return type of scsi_queue_insert() from int to void.
- Added a cancel_work_sync(&sdev->requeue_work) call in
  __scsi_remove_device().

Changes compared to v5:
- Removed the function scsi_free_queue() and inlined that function
  in its callers.
- Added two additional patches.