From: Yu Kuai <[email protected]>
This RFC remains a preparatory series for the blkcg_mutex conversion
proposed in the related blkcg_mutex RFC v2 series [1]. That conversion
moves queue-local blkg topology synchronization from q->queue_lock to
q->blkcg_mutex, which is awkward while bios directly store queue-local
blkg references.
v1 made the stored bio association queue-independent by replacing bi_blkg
with bi_blkcg, but a bio-owned blkg reference still had to be recovered by
looking up the bio's blkcg and current request_queue. Tao Cui reported that
cgroup removal deletes a dying blkg from the per-blkcg radix tree before a
throttled bio drops its reference. A later lookup for that pinned blkg then
fails, triggers the warning in bio_pinned_blkg(), and leaks the reference.
v2 makes request_queue the authoritative lookup owner before converting the
bio association. A queue-owned rhashtable, keyed by the blkcg CSS ID, keeps
dying blkgs discoverable until their references drain while q->blkg_list
remains available for ordered walks. The bio conversion then stores and
pins the blkcg CSS, lazily creates a blkg only for users which need one, and
uses lookup-only access for completion and accounting paths which already
own a blkg reference. Async bio punt state is finally moved from blkg to
blkcg so punting alone does not instantiate a queue-local blkg.
Changes since v1:
- Add patch 1 to wait for every old blkg to leave q->blkg_list before a
shared request_queue is rebound, instead of treating root_blkg == NULL
as completion of asynchronous blkg teardown.
- Add patch 2 to replace the per-blkcg radix tree and lookup hint with a
request_queue rhashtable keyed by blkcg->css.id, as suggested by
Christoph Hellwig. Keep dying pinned blkgs in the hash until
blkg_release() so bio-owned references remain discoverable.
- Fold the v1 helper-only patch into patch 3, as suggested by Jan Kara and
Christoph Hellwig, and make bio_blkcg() naturally return NULL for an
unassociated bio.
- Rework patch 3 so blkg_lookup_create() acquires the bio-owned reference,
falls back to a live parent when creation or tryget fails, and updates
bi_blkcg when the returned blkg belongs to an ancestor.
- Make bio_blkg_lookup() lookup-only: it returns NULL unless BIO_BLKG_REF
is already set. Use bio_blkg() in the BFQ and IOCOST merge paths which
may need to create a blkg, while keeping blk_cgroup_bio_start() and
completion paths lookup-only.
- Move CSS online-reference handling into
bio_associate_blkcg_from_css(), including fallback to the root blkcg, so
bio_associate_blkcg() does not take a redundant reference.
- Keep the v1 async bio punt conversion as patch 4 and document that
async_bio_lock protects async_bios.
Previous versions:
v1: https://lore.kernel.org/r/[email protected]
Related series:
[1] RFC v2 blk-cgroup: protect blkgs with blkcg_mutex
https://lore.kernel.org/r/[email protected]
Yu Kuai (4):
blk-cgroup: wait for old blkgs to leave queue before disk rebind
blk-cgroup: use a request_queue rhashtable for blkg lookup
blk-cgroup: store blkcg in bio instead of blkg
blk-cgroup: move async bio punt state to blkcg
Documentation/admin-guide/cgroup-v2.rst | 2 +-
block/bfq-cgroup.c | 16 +-
block/bfq-iosched.c | 19 +-
block/bio.c | 22 +-
block/blk-cgroup-fc-appid.c | 10 +-
block/blk-cgroup.c | 348 ++++++++++++++----------
block/blk-cgroup.h | 82 ++++--
block/blk-core.c | 9 +-
block/blk-crypto-fallback.c | 2 +-
block/blk-iocost.c | 12 +-
block/blk-iolatency.c | 11 +-
block/blk-ioprio.c | 2 +-
block/blk-throttle.c | 2 +-
block/blk-throttle.h | 2 +-
drivers/md/bcache/request.c | 2 +-
drivers/md/dm.c | 2 +-
drivers/md/md.c | 2 +-
drivers/nvdimm/nd_virtio.c | 2 +-
fs/gfs2/lops.c | 3 +-
include/linux/bio.h | 26 +-
include/linux/blk_types.h | 9 +-
include/linux/blkdev.h | 2 +
include/linux/writeback.h | 2 +-
mm/page_io.c | 13 +-
24 files changed, 357 insertions(+), 245 deletions(-)
base-commit: f2690679ecf3a3151688ebef766dd2512ff95854
--
2.51.0
