From: Tejun Heo <tj@kernel.org>
To: Muchun Song <songmuchun@bytedance.com>
Cc: viro@zeniv.linux.org.uk, axboe@fb.com, willy@infradead.org,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
duanxiongchun@bytedance.com, Michal Hocko <mhocko@suse.com>
Subject: Re: [PATCH v3] writeback: fix obtain a reference to a freeing memcg css
Date: Sun, 4 Apr 2021 14:01:26 -0400 [thread overview]
Message-ID: <YGn+9gY/VAc6YI/q@mtj.duckdns.org> (raw)
In-Reply-To: <20210402091145.80635-1-songmuchun@bytedance.com>
On Fri, Apr 02, 2021 at 05:11:45PM +0800, Muchun Song wrote:
> The caller of wb_get_create() should pin the memcg, because
> wb_get_create() relies on this guarantee. The rcu read lock
> only can guarantee that the memcg css returned by css_from_id()
> cannot be released, but the reference of the memcg can be zero.
>
> rcu_read_lock()
> memcg_css = css_from_id()
> wb_get_create(memcg_css)
> cgwb_create(memcg_css)
> // css_get can change the ref counter from 0 back to 1
> css_get(memcg_css)
> rcu_read_unlock()
>
> Fix it by holding a reference to the css before calling
> wb_get_create(). This is not a problem I encountered in the
> real world. Just the result of a code review.
>
> Fixes: 682aa8e1a6a1 ("writeback: implement unlocked_inode_to_wb transaction and use it for stat updates")
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Tejun Heo <tj@kernel.org>
Thanks.
--
tejun
next prev parent reply other threads:[~2021-04-04 18:01 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-02 9:11 [PATCH v3] writeback: fix obtain a reference to a freeing memcg css Muchun Song
2021-04-04 18:01 ` Tejun Heo [this message]
2021-05-20 3:45 ` Muchun Song
2021-06-28 16:32 ` Jan Kara
2021-06-29 3:06 ` [External] " Muchun Song
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