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Subject[PATCH V4 0/2] fixes for the updating nr_hw_queues
Hi Jens

Two fixes for updating nr_hw_queues.

The first patch fixes the following scenario:
io scheduler (kyber) depends on the mapping between ctx and hctx.
When update nr_hw_queues, io scheduler's init_hctx will be
invoked before the mapping is adapted correctly, this would cause
panic in kyber.

The second patch fixes the following scenario:
part_in_flight/rw will invoke blk_mq_in_flight/rw to account the
inflight requests. It will access the queue_hw_ctx and nr_hw_queues
w/o any protection. When updating nr_hw_queues and blk_mq_in_flight
/rw occur concurrently, panic comes up.

- remove the elv_type in request_queue and introduce blk_mq_qe_pair
to cache the elevator_type associated with one request_queue. And
add two new helper interfaces blk_mq_elv_switch_none/back to carry
out the elevator_type caching and switching work.
- Add Ming's Reviewd-by on 2nd patch and remove it from 1st patch due
to the reworking.
- comment modification.

- move the rcu and q_usage_counter checking into blk_mq_queue_tag_busy_iter
as suggestion of Ming.
- Add more comment about the __module_get in 1st patch.
- Add Ming's Reviewd-by on 1st patch.

- remove blk_mq_sched_init/exit_hctx in patch 1.
- use q_usage_counter instead of adding new member suggested by
Ming in patch 2.
- comment modification.

block/blk-mq-sched.c | 44 --------------------------------------------
block/blk-mq-sched.h | 5 -----
block/blk-mq-tag.c | 14 +++++++++++++-
block/blk-mq.c | 96 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--------
block/blk.h | 2 ++
block/elevator.c | 20 ++++++++++++--------
6 files changed, 115 insertions(+), 66 deletions(-)


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