Messages in this thread | | | Date | Sun, 4 Apr 2021 14:01:26 -0400 | From | Tejun Heo <> | Subject | Re: [PATCH v3] writeback: fix obtain a reference to a freeing memcg css |
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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
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