[PATCH V3 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 introduces preempt freez, and tries to solve the issue
by preempt freezing block queue during SCSI quiesce, and allows
to allocate request of RQF_PREEMPT when queue is preempt-frozen.

Both SCSI and SCSI_MQ have this IO deadlock issue, this patch fixes
them all by introducing blk_freeze_queue_preempt() and
blk_unfreeze_queue_preempt(), also unifying current interfaces for
freezing queue between block legacy and blk-mq.

Oleksandr has verified that this patchset V2 fixes his I/O hang
during suspend/resume cycle.

V3:
	- introduce q->preempt_unfreezing to fix one bug of preempt freeze
	- call blk_queue_enter_live() only when queue is preempt frozen
	- cleanup a bit on the implementation of preempt freeze
	- only patch 6 and 7 are changed

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: introduce preempt version of blk_[freeze|unfreeze]_queue
  block: allow to allocate req with REQF_PREEMPT when queue is preempt
    frozen
  SCSI: preempt freeze block queue when SCSI device is put into quiesce

 block/bfq-iosched.c      |   2 +-
 block/blk-cgroup.c       |   8 +--
 block/blk-core.c         |  53 ++++++++++++---
 block/blk-mq.c           | 170 +++++++++++++++++++++++++++++++++++++++--------
 block/blk-mq.h           |   1 -
 block/blk.h              |  17 +++++
 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  |  22 +++++-
 include/linux/blk-mq.h   |  15 +++--
 include/linux/blkdev.h   |  21 +++++-
 13 files changed, 273 insertions(+), 66 deletions(-)

-- 
2.9.5