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

["yu kuai" <yukuai@fygo.io>]

Friendly ping ...

This set can still be applied cleanly for block-7.2 branch.

在 2026/6/8 11:42, Yu Kuai 写道:
> 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

-- 
Thanks,
Kuai