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(-) -- 2.9.5
