From 6281beee5bb9c6d1756080052a9f989d387cf466 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 14 Mar 2022 14:30:11 -1000 Subject: [PATCH] block: don't merge across cgroup boundaries if blkcg is enabled commit 6b2b04590b51aa4cf395fcd185ce439cab5961dc upstream. blk-iocost and iolatency are cgroup aware rq-qos policies but they didn't disable merges across different cgroups. This obviously can lead to accounting and control errors but more importantly to priority inversions - e.g. an IO which belongs to a higher priority cgroup or IO class may end up getting throttled incorrectly because it gets merged to an IO issued from a low priority cgroup. Fix it by adding blk_cgroup_mergeable() which is called from merge paths and rejects cross-cgroup and cross-issue_as_root merges. Signed-off-by: Tejun Heo Fixes: d70675121546 ("block: introduce blk-iolatency io controller") Cc: stable@vger.kernel.org # v4.19+ Cc: Josef Bacik Link: https://lore.kernel.org/r/Yi/eE/6zFNyWJ+qd@slm.duckdns.org Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman --- block/blk-merge.c | 12 ++++++++++++ include/linux/blk-cgroup.h | 17 +++++++++++++++++ 2 files changed, 29 insertions(+) diff --git a/block/blk-merge.c b/block/blk-merge.c index 7efa8c3e2b72..8054410536fd 100644 --- a/block/blk-merge.c +++ b/block/blk-merge.c @@ -7,6 +7,8 @@ #include #include #include +#include +#include #include @@ -486,6 +488,9 @@ static inline int ll_new_hw_segment(struct request_queue *q, if (req->nr_phys_segments + nr_phys_segs > queue_max_segments(q)) goto no_merge; + if (!blk_cgroup_mergeable(req, bio)) + goto no_merge; + if (blk_integrity_merge_bio(q, req, bio) == false) goto no_merge; @@ -609,6 +614,9 @@ static int ll_merge_requests_fn(struct request_queue *q, struct request *req, if (total_phys_segments > queue_max_segments(q)) return 0; + if (!blk_cgroup_mergeable(req, next->bio)) + return 0; + if (blk_integrity_merge_rq(q, req, next) == false) return 0; @@ -843,6 +851,10 @@ bool blk_rq_merge_ok(struct request *rq, struct bio *bio) if (rq->rq_disk != bio->bi_disk || req_no_special_merge(rq)) return false; + /* don't merge across cgroup boundaries */ + if (!blk_cgroup_mergeable(rq, bio)) + return false; + /* only merge integrity protected bio into ditto rq */ if (blk_integrity_merge_bio(rq->q, rq, bio) == false) return false; diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h index 6d766a19f2bb..8f1be8b49391 100644 --- a/include/linux/blk-cgroup.h +++ b/include/linux/blk-cgroup.h @@ -21,6 +21,7 @@ #include #include #include +#include /* percpu_counter batch for blkg_[rw]stats, per-cpu drift doesn't matter */ #define BLKG_STAT_CPU_BATCH (INT_MAX / 2) @@ -844,6 +845,21 @@ static inline void blkcg_use_delay(struct blkcg_gq *blkg) atomic_inc(&blkg->blkcg->css.cgroup->congestion_count); } +/** + * blk_cgroup_mergeable - Determine whether to allow or disallow merges + * @rq: request to merge into + * @bio: bio to merge + * + * @bio and @rq should belong to the same cgroup and their issue_as_root should + * match. The latter is necessary as we don't want to throttle e.g. a metadata + * update because it happens to be next to a regular IO. + */ +static inline bool blk_cgroup_mergeable(struct request *rq, struct bio *bio) +{ + return rq->bio->bi_blkg == bio->bi_blkg && + bio_issue_as_root_blkg(rq->bio) == bio_issue_as_root_blkg(bio); +} + static inline int blkcg_unuse_delay(struct blkcg_gq *blkg) { int old = atomic_read(&blkg->use_delay); @@ -947,6 +963,7 @@ static inline struct request_list *blk_rq_rl(struct request *rq) { return &rq->q static inline bool blkcg_bio_issue_check(struct request_queue *q, struct bio *bio) { return true; } +static inline bool blk_cgroup_mergeable(struct request *rq, struct bio *bio) { return true; } #define blk_queue_for_each_rl(rl, q) \ for ((rl) = &(q)->root_rl; (rl); (rl) = NULL)