[PATCH v4 0/7] blk-mq: fix race conditions on cpu hotplug handling

[Akinobu Mita <akinobu.mita@gmail.com>]

This patchset addresses several race conditions on cpu hotplug handling
for blk-mq.  All problems can be reproducible by the following script.

while true; do
	echo 0 > /sys/devices/system/cpu/cpu1/online
	echo 1 > /sys/devices/system/cpu/cpu1/online
done &

while true; do
	modprobe -r null_blk
	modprobe null_blk queue_mode=2 irqmode=1
	sleep 0.1
done

* Changes from v3
- Rebased to the latest kernel
- Add Reviewed-by tags

* Changes from v2
- Add regression fix for hctx->tags->cpumask
- Remove BLK_MQ_F_SYSFS_UP per-hctx flag and use mq_sysfs_init_done
  per-queue flag instead with appropriate locking in order to keep
  track of 'mq' sysfs entry's life
- Add comments on non-trivial stuffs, suggested by Ming

* Changes from v1
- Release q->mq_map in blk_mq_release()
- Fix deadlock when reading cpu_list
- Fix race freeze and unfreeze

Akinobu Mita (7):
  blk-mq: avoid setting hctx->tags->cpumask before allocation
  blk-mq: fix sysfs registration/unregistration race
  blk-mq: Fix use after of free q->mq_map
  blk-mq: fix q->mq_usage_counter access race
  blk-mq: avoid inserting requests before establishing new mapping
  blk-mq: fix freeze queue race
  blk-mq: fix deadlock when reading cpu_list

 block/blk-core.c       |   1 +
 block/blk-mq-cpumap.c  |   9 +++--
 block/blk-mq-sysfs.c   |  36 ++++++++++++------
 block/blk-mq.c         | 100 +++++++++++++++++++++++++++++++++++++------------
 block/blk-mq.h         |   3 +-
 include/linux/blk-mq.h |   1 -
 include/linux/blkdev.h |   8 ++++
 7 files changed, 116 insertions(+), 42 deletions(-)

Cc: Jens Axboe <axboe@kernel.dk>
Cc: Ming Lei <tom.leiming@gmail.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Keith Busch <keith.busch@intel.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Wanpeng Li <wanpeng.li@hotmail.com>
-- 
1.9.1