Re: [PATCH V7 0/6] block/scsi: safe SCSI quiescing

Martin Steigerwald
2017-09-30T09:47:17Z

Hi Ming.

Ming Lei - 30.09.17, 14:12:
> 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.

Isn´t that material for -stable as well?

I´d love to see this go into 4.14. Especially as its an LTS release.

Thanks,
Martin

> 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.
>
> 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
>
> Ming Lei (6):
> blk-mq: only run hw queues for blk-mq
> block: tracking request allocation with q_usage_counter
> block: pass flags to blk_queue_enter()
> block: prepare for passing RQF_PREEMPT to request allocation
> block: support PREEMPT_ONLY
> SCSI: set block queue at preempt only when SCSI device is put into
> quiesce
>
> block/blk-core.c | 63
> +++++++++++++++++++++++++++++++++++++++---------- block/blk-mq.c |
> 14 ++++-------
> block/blk-timeout.c | 2 +-
> drivers/scsi/scsi_lib.c | 25 +++++++++++++++++---
> fs/block_dev.c | 4 ++--
> include/linux/blk-mq.h | 7 +++---
> include/linux/blkdev.h | 27 ++++++++++++++++++---
> 7 files changed, 107 insertions(+), 35 deletions(-)

--
Martin