[PATCH 0/8] blk-cgroup: remove queue_lock nesting from blkcg paths

[Yu Kuai <yukuai@kernel.org>]

From: Yu Kuai <yukuai@fygo.io>

Hi,

This series is the follow-up blk-cgroup locking cleanup on top of the
earlier blkg-list protection fixes, and prepares blk-cgroup to stop using
q->queue_lock as the global blkg lifetime/iteration lock.

The current queue_lock based protection is hard to maintain because
queue_lock is used from hardirq and softirq completion paths, while some
blkcg cgroup file paths also need to iterate blkgs, print policy data, or
create blkgs from RCU-protected contexts.  This series first tightens the
blkcg-side lifetime rules:

- blkcg_print_stat() iterates blkgs under blkcg->lock with IRQs disabled.
- policy data freeing is delayed past an RCU grace period.
- blkcg_print_blkgs(), blkg lookup/create, bio association, page-IO
  association, blkg destruction, and BFQ initialization stop nesting
  queue_lock under RCU or blkcg->lock.

Using blkcg->lock and RCU for blkcg-owned lists/data keeps the lock order
local to blk-cgroup and avoids extending queue_lock into cgroup file
iteration paths.  It also makes the subsequent conversion to q->blkcg_mutex
possible without carrying forward queue_lock's interrupt-context
constraints.

Yu Kuai (8):
  blk-cgroup: protect iterating blkgs with blkcg->lock in
    blkcg_print_stat()
  blk-cgroup: delay freeing policy data after rcu grace period
  blk-cgroup: don't nest queue_lock under rcu in blkcg_print_blkgs()
  blk-cgroup: don't nest queue_lock under rcu in blkg_lookup_create()
  blk-cgroup: don't nest queue_lock under rcu in bio_associate_blkg()
  blk-cgroup: don't nest queue_lock under blkcg->lock in
    blkcg_destroy_blkgs()
  mm/page_io: don't nest queue_lock under rcu in
    bio_associate_blkg_from_page()
  block, bfq: don't grab queue_lock to initialize bfq

 block/bfq-cgroup.c        |  17 ++++-
 block/bfq-iosched.c       |   5 --
 block/blk-cgroup-rwstat.c |  15 ++--
 block/blk-cgroup.c        | 151 ++++++++++++++++++++++----------------
 block/blk-cgroup.h        |   8 +-
 block/blk-iocost.c        |  22 ++++--
 block/blk-iolatency.c     |  10 ++-
 block/blk-throttle.c      |  13 +++-
 mm/page_io.c              |   7 +-
 9 files changed, 158 insertions(+), 90 deletions(-)


base-commit: b23df513de562739af61fa61ba80ef5e8059a636
-- 
2.51.0