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
