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Date: Thu, 8 Dec 2022 17:01:40 -0500 From: Waiman Long <longman@...hat.com> To: Jens Axboe <axboe@...nel.dk>, Tejun Heo <tj@...nel.org>, Josef Bacik <josef@...icpanda.com>, Zefan Li <lizefan.x@...edance.com>, Johannes Weiner <hannes@...xchg.org>, Andrew Morton <akpm@...ux-foundation.org> Cc: cgroups@...r.kernel.org, linux-block@...r.kernel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org, Michal Koutný <mkoutny@...e.com>, "Dennis Zhou (Facebook)" <dennisszhou@...il.com>, Waiman Long <longman@...hat.com> Subject: [PATCH-block 2/3] blk-cgroup: Don't flush a blkg if destroyed Before commit 3b8cc6298724 ("blk-cgroup: Optimize blkcg_rstat_flush()"), blkg's stats is only flushed if they are online. In addition, the stat flushing of blkgs in blkcg_rstat_flush() includes propagating the rstat data to its parent. However, if a blkg has been destroyed (offline), the validity of its parent may be questionable. For safety, revert back to the old behavior by ignoring offline blkg's. Signed-off-by: Waiman Long <longman@...hat.com> --- block/blk-cgroup.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index 21cc88349f21..c466aef0d467 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -885,6 +885,12 @@ static void blkcg_rstat_flush(struct cgroup_subsys_state *css, int cpu) WRITE_ONCE(bisc->lqueued, false); + /* Don't flush its stats if blkg is offline */ + if (unlikely(!blkg->online)) { + percpu_ref_put(&blkg->refcnt); + continue; + } + /* fetch the current per-cpu values */ do { seq = u64_stats_fetch_begin(&bisc->sync); -- 2.31.1
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