Re: [PATCH V4 0/10] block/scsi: safe SCSI quiescing

[Cathy Avery <cavery@redhat.com>]

On 09/11/2017 07:10 AM, Ming Lei wrote:
> 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 comming, 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 wait forever,
> meantime scsi_device_resume() waits for completion of RQF_PREEMPT,
> then system hangs forever, such as during system suspend or
> sending SCSI domain alidation.
>
> Both IO hang inside system suspend[1] or SCSI domain validation
> were reported before.
>
> This patch introduces preempt freeze, and solves the issue
> by preempt freezing block queue during SCSI quiesce, and allows
> to allocate request of RQF_PREEMPT when queue is in this state.
>
> Oleksandr verified that V3 does fix the hang during suspend/resume,
> and Cathy verified that revised V3 fixes hang in sending
> SCSI domain validation.
>
> Both SCSI and SCSI_MQ have this IO deadlock issue, this patch fixes
> them all by introducing/unifying blk_freeze_queue_preempt() and
> blk_unfreeze_queue_preempt(), and cleanup is done together.
>
> The patchset can be found in the following gitweb:
>
> 	https://github.com/ming1/linux/tree/blk_safe_scsi_quiesce_V4
>
> V4:
> 	- reorganize patch order to make it more reasonable
> 	- support nested preempt freeze, as required by SCSI transport spi
> 	- check preempt freezing in slow path of of blk_queue_enter()
> 	- add "SCSI: transport_spi: resume a quiesced device"
> 	- wake up freeze queue in setting dying for both blk-mq and legacy
> 	- rename blk_mq_[freeze|unfreeze]_queue() in one patch
> 	- rename .mq_freeze_wq and .mq_freeze_depth
> 	- improve comment
>
> 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
>
>
> Thanks,
> Ming
>
>
> Ming Lei (10):
>    blk-mq: only run hw queues for blk-mq
>    block: tracking request allocation with q_usage_counter
>    blk-mq: rename blk_mq_[freeze|unfreeze]_queue
>    blk-mq: rename blk_mq_freeze_queue_wait as blk_freeze_queue_wait
>    block: rename .mq_freeze_wq and .mq_freeze_depth
>    block: pass flags to blk_queue_enter()
>    block: introduce preempt version of blk_[freeze|unfreeze]_queue
>    block: allow to allocate req with RQF_PREEMPT when queue is preempt
>      frozen
>    SCSI: transport_spi: resume a quiesced device
>    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                  |  95 ++++++++++++++++----
>   block/blk-mq.c                    | 180 ++++++++++++++++++++++++++++----------
>   block/blk-mq.h                    |   1 -
>   block/blk-timeout.c               |   2 +-
>   block/blk.h                       |  12 +++
>   block/elevator.c                  |   4 +-
>   drivers/block/loop.c              |  24 ++---
>   drivers/block/rbd.c               |   2 +-
>   drivers/nvme/host/core.c          |   8 +-
>   drivers/scsi/scsi_lib.c           |  25 +++++-
>   drivers/scsi/scsi_transport_spi.c |   3 +
>   fs/block_dev.c                    |   4 +-
>   include/linux/blk-mq.h            |  15 ++--
>   include/linux/blkdev.h            |  32 +++++--
>   16 files changed, 313 insertions(+), 104 deletions(-)
>

I've tested this patch set for spi_transport issuing a domain validation 
under low blk_request conditions.

Tested-by: Cathy Avery <cavery@redhat.com>