From: Tejun Heo <tj@kernel.org>
To: Ming Lei <ming.lei@redhat.com>
Cc: "Waiman Long" <longman@redhat.com>,
"Jens Axboe" <axboe@kernel.dk>,
"Josef Bacik" <josef@toxicpanda.com>,
"Zefan Li" <lizefan.x@bytedance.com>,
"Johannes Weiner" <hannes@cmpxchg.org>,
"Andrew Morton" <akpm@linux-foundation.org>,
cgroups@vger.kernel.org, linux-block@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
"Michal Koutný" <mkoutny@suse.com>,
"Dennis Zhou (Facebook)" <dennisszhou@gmail.com>
Subject: Re: [PATCH v4 2/2] blk-cgroup: Flush stats at blkgs destruction path
Date: Thu, 2 Feb 2023 12:35:08 -1000 [thread overview]
Message-ID: <Y9w6nDJoekdCYZXr@slm.duckdns.org> (raw)
In-Reply-To: <Y9s4+Nop1eluWmJ4@T590>
On Thu, Feb 02, 2023 at 12:15:52PM +0800, Ming Lei wrote:
> > @@ -1093,6 +1095,20 @@ static void blkcg_destroy_blkgs(struct blkcg *blkcg)
> >
> > might_sleep();
> >
> > + /*
> > + * Flush all the non-empty percpu lockless lists to release the
> > + * blkg references held by those lists which, in turn, will
> > + * allow those blkgs to be freed and release their references to
> > + * blkcg. Otherwise, they may not be freed at all becase of this
> > + * circular dependency resulting in memory leak.
> > + */
> > + for_each_possible_cpu(cpu) {
> > + struct llist_head *lhead = per_cpu_ptr(blkcg->lhead, cpu);
> > +
> > + if (!llist_empty(lhead))
> > + cgroup_rstat_css_cpu_flush(&blkcg->css, cpu);
> > + }
>
> I guess it is possible for new iostat_cpu to be added just after the
> llist_empty() check.
Ah, good point. Maybe:
* Move flush below the blkg kill loop.
* In blk_cgroup_bio_start(), use percpu_ref_tryget() to decide whether to
add to llist or not.
--
tejun
next prev parent reply other threads:[~2023-02-02 22:35 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-15 3:31 [PATCH v4 0/2] blk-cgroup: Fix potential UAF & flush rstat at blkgs destruction path Waiman Long
2022-12-15 3:31 ` [PATCH v4 1/2] bdi, blk-cgroup: Fix potential UAF of blkcg Waiman Long
2022-12-15 3:31 ` [PATCH v4 2/2] blk-cgroup: Flush stats at blkgs destruction path Waiman Long
2023-02-02 4:15 ` Ming Lei
2023-02-02 22:35 ` Tejun Heo [this message]
2023-02-02 3:26 ` [PATCH v4 0/2] blk-cgroup: Fix potential UAF & flush rstat " Waiman Long
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