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    SubjectRe: [PATCH V8 0/8] block/scsi: safe SCSI quiescing
    Hi Ming, Jens.

    What is the fate of this patchset please?

    03.10.2017 16:03, Ming Lei wrote:
    > Hi Jens,
    >
    > Please consider this patchset for V4.15, and it fixes one
    > kind of long-term I/O hang issue in either block legacy path
    > or blk-mq.
    >
    > 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,
    > then system hangs forever, such as during system suspend or
    > sending SCSI domain alidation in case of transport_spi.
    >
    > Both IO hang inside system suspend[1] or SCSI domain validation
    > were reported before.
    >
    > This patch introduces preempt only mode, and solves the issue
    > by allowing RQF_PREEMP only during SCSI quiesce.
    >
    > Both SCSI and SCSI_MQ have this IO deadlock issue, this patch fixes
    > them all.
    >
    > V8:
    > - fix one race as pointed out by Bart
    > - pass 'op' to blk_queue_enter() as suggested by Christoph
    >
    > V7:
    > - add Reviewed-by & Tested-by
    > - one line change in patch 5 for checking preempt request
    >
    > V6:
    > - borrow Bart's idea of preempt only, with clean
    > implementation(patch 5/patch 6)
    > - needn't any external driver's dependency, such as MD's
    > change
    >
    > V5:
    > - fix one tiny race by introducing blk_queue_enter_preempt_freeze()
    > given this change is small enough compared with V4, I added
    > tested-by directly
    >
    > 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
    >
    > Bart Van Assche (1):
    > block: Convert RQF_PREEMPT into REQ_PREEMPT
    >
    > Ming Lei (7):
    > blk-mq: only run hw queues for blk-mq
    > block: tracking request allocation with q_usage_counter
    > block: pass 'op' to blk_queue_enter()
    > percpu-refcount: introduce __percpu_ref_tryget_live
    > blk-mq: return if queue is frozen via current blk_freeze_queue_start
    > block: support PREEMPT_ONLY
    > SCSI: set block queue at preempt only when SCSI device is put into
    > quiesce
    >
    > block/blk-core.c | 66
    > +++++++++++++++++++++++++++++++++++++----
    > block/blk-mq-debugfs.c | 2 +-
    > block/blk-mq.c | 26 ++++++++--------
    > block/blk-mq.h | 1 -
    > block/blk-timeout.c | 2 +-
    > block/blk.h | 2 +-
    > drivers/ide/ide-atapi.c | 3 +-
    > drivers/ide/ide-io.c | 2 +-
    > drivers/ide/ide-pm.c | 4 +--
    > drivers/scsi/scsi_lib.c | 31 +++++++++++++++----
    > fs/block_dev.c | 4 +--
    > include/linux/blk-mq.h | 4 +--
    > include/linux/blk_types.h | 6 ++++
    > include/linux/blkdev.h | 10 ++++---
    > include/linux/percpu-refcount.h | 27 ++++++++++-------
    > 15 files changed, 137 insertions(+), 53 deletions(-)

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