From 4308a434e5e08c78676aa66bc626ef78cbef0883 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Wed, 24 Jul 2019 10:37:55 -0700 Subject: [PATCH] blkcg: don't offline parent blkcg first blkcg->cgwb_refcnt is used to delay blkcg offlining so that blkgs don't get offlined while there are active cgwbs on them. However, it ends up making offlining unordered sometimes causing parents to be offlined before children. Let's fix this by making child blkcgs pin the parents' online states. Note that pin/unpin names are chosen over get/put intentionally because css uses get/put online for something different. Signed-off-by: Tejun Heo Signed-off-by: Jens Axboe --- block/blk-cgroup.c | 16 ++++++++++++++++ include/linux/blk-cgroup.h | 6 +++++- 2 files changed, 21 insertions(+), 1 deletion(-) diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index 2acef6a649541c..c5dc833212e1d1 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -1006,6 +1006,21 @@ blkcg_css_alloc(struct cgroup_subsys_state *parent_css) return ret; } +static int blkcg_css_online(struct cgroup_subsys_state *css) +{ + struct blkcg *blkcg = css_to_blkcg(css); + struct blkcg *parent = blkcg_parent(blkcg); + + /* + * blkcg_pin_online() is used to delay blkcg offline so that blkgs + * don't go offline while cgwbs are still active on them. Pin the + * parent so that offline always happens towards the root. + */ + if (parent) + blkcg_pin_online(parent); + return 0; +} + /** * blkcg_init_queue - initialize blkcg part of request queue * @q: request_queue to initialize @@ -1199,6 +1214,7 @@ static void blkcg_exit(struct task_struct *tsk) struct cgroup_subsys io_cgrp_subsys = { .css_alloc = blkcg_css_alloc, + .css_online = blkcg_css_online, .css_offline = blkcg_css_offline, .css_free = blkcg_css_free, .can_attach = blkcg_can_attach, diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h index 7fb7caa55a3d20..35f8ffe92b702b 100644 --- a/include/linux/blk-cgroup.h +++ b/include/linux/blk-cgroup.h @@ -436,8 +436,12 @@ static inline void blkcg_pin_online(struct blkcg *blkcg) */ static inline void blkcg_unpin_online(struct blkcg *blkcg) { - if (refcount_dec_and_test(&blkcg->online_pin)) + do { + if (!refcount_dec_and_test(&blkcg->online_pin)) + break; blkcg_destroy_blkgs(blkcg); + blkcg = blkcg_parent(blkcg); + } while (blkcg); } /**