Hello Jens,

Replace the spinlock in blk_mq_find_and_get_req() with an SRCU read lock
around the tag iterators.

Avoids scsi_host_busy() lockup during scsi host blocked  in case of big cpu
cores & deep queue depth.

Also it becomes possible to use blk_mq_in_driver_rw() for io accounting now.

Take the following approach:

- clearing rq reference in tags->rqs[] and deferring freeing scheduler requests
in SRCU callback

- replace tags->lock with srcu read lock in tags iterator.


Ming Lei (5):
  blk-mq: Move flush queue allocation into blk_mq_init_hctx()
  blk-mq: Pass tag_set to blk_mq_free_rq_map/tags
  blk-mq: Defer freeing of tags page_list to SRCU callback
  blk-mq: Defer freeing flush queue to SRCU callback
  blk-mq: Replace tags->lock with SRCU for tag iterators

 block/blk-mq-sched.c   |  4 +-
 block/blk-mq-sysfs.c   |  1 -
 block/blk-mq-tag.c     | 38 +++++++++++++++---
 block/blk-mq.c         | 87 +++++++++++++++++++++---------------------
 block/blk-mq.h         |  4 +-
 block/blk.h            |  1 +
 include/linux/blk-mq.h |  2 +
 7 files changed, 82 insertions(+), 55 deletions(-)

-- 
2.47.0