[PATCH V2 0/8] block/scsi: safe SCSI quiescing

[Ming Lei <ming.lei@redhat.com>]

Hi,

The current SCSI quiesce isn't safe and easy to trigger I/O deadlock.

Once SCSI device is put into QUIESCE, no new request except for RQF_PREEMPT
can be dispatched to SCSI successfully, and scsi_device_quiesce() just simply
waits for completion of I/Os dispatched to SCSI stack. It isn't enough at all.

Because new request still can be allocated, but all the allocated
requests can't be dispatched successfully, so request pool can be
consumed up easily.

Then request with RQF_PREEMPT can't be allocated, and system may
hang forever, such as during system suspend or SCSI domain alidation.

Both IO hang inside system suspend[1] or SCSI domain validation
were reported before.

This patch tries to solve the issue by freezing block queue during
SCSI quiescing, and allowing to allocate request of RQF_PREEMPT
when queue is frozen.

Both SCSI and SCSI_MQ have this IO deadlock issue, this patch fixes
them all by introducing preempt version of blk_freeze_queue() and
blk_unfreeze_queue().

V2:
	- drop the 1st patch in V1 because percpu_ref_is_dying() is
	enough as pointed by Tejun

	- introduce preempt version of blk_[freeze|unfreeze]_queue

	- sync between preempt freeze and normal freeze

	- fix warning from percpu-refcount as reported by Oleksandr



[1] https://marc.info/?t=150340250100013&r=3&w=2



Ming Lei (8):
  blk-mq: rename blk_mq_unfreeze_queue as blk_unfreeze_queue
  blk-mq: rename blk_mq_freeze_queue as blk_freeze_queue
  blk-mq: only run hw queues for blk-mq
  blk-mq: rename blk_mq_freeze_queue_wait as blk_freeze_queue_wait
  block: tracking request allocation with q_usage_counter
  block: allow to allocate req with REQF_PREEMPT when queue is frozen
  block: introduce preempt version of blk_[freeze|unfreeze]_queue
  SCSI: freeze block queue when SCSI device is put into quiesce

 block/bfq-iosched.c      |   2 +-
 block/blk-cgroup.c       |   8 ++--
 block/blk-core.c         |  50 ++++++++++++++++----
 block/blk-mq.c           | 119 ++++++++++++++++++++++++++++++++++++-----------
 block/blk-mq.h           |   1 -
 block/blk.h              |   6 +++
 block/elevator.c         |   4 +-
 drivers/block/loop.c     |  16 +++----
 drivers/block/rbd.c      |   2 +-
 drivers/nvme/host/core.c |   8 ++--
 drivers/scsi/scsi_lib.c  |  21 ++++++++-
 include/linux/blk-mq.h   |  15 +++---
 include/linux/blkdev.h   |  20 +++++++-
 13 files changed, 206 insertions(+), 66 deletions(-)

-- 
2.9.5