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

Oleksandr Natalenko
2017-08-31T17:34:06Z

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(-)