Re: [PATCH 0/9] block/scsi: safe SCSI quiescing

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Since I'm in CC, does this series aim to replace 2 patches I've tested before:

blk-mq: add requests in the tail of hctx->dispatch
blk-mq: align to legacy's implementation of blk_execute_rq

?

On čtvrtek 31. srpna 2017 19:27:19 CEST Ming Lei wrote:
> 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 unifying blk_freeze_queue() and blk_unfreeze_queue().
> 
> 
> [1] https://marc.info/?t=150340250100013&r=3&w=2
> 
> Ming Lei (9):
>   percpu-refcount: introduce percpu_ref_is_dead()
>   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
>   block: introduce blk_drain_queue()
>   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
>   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                | 49
> +++++++++++++++++++++++++++++++++-------- block/blk-mq.c                  |
> 49 +++++++++++++++++++++-------------------- block/blk-mq.h                
>  |  1 -
>  block/blk.h                     |  5 +++++
>  block/elevator.c                |  4 ++--
>  drivers/block/loop.c            | 16 +++++++-------
>  drivers/block/rbd.c             |  2 +-
>  drivers/ide/ide-pm.c            |  3 ++-
>  drivers/nvme/host/core.c        |  8 +++----
>  drivers/scsi/scsi_lib.c         | 23 +++++++++++++++++--
>  include/linux/blk-mq.h          | 13 ++++++-----
>  include/linux/blkdev.h          | 18 +++++++++++++--
>  include/linux/percpu-refcount.h | 17 ++++++++++++++
>  15 files changed, 153 insertions(+), 65 deletions(-)




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