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Mon, 03 Aug 2020 08:04:53 -0700 (PDT) Date: Mon, 3 Aug 2020 11:03:49 -0400 From: Johannes Weiner To: Michal Hocko Cc: Roman Gushchin , Andrew Morton , Christoph Lameter , Shakeel Butt , linux-mm@kvack.org, Vlastimil Babka , kernel-team@fb.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v7 05/19] mm: memcontrol: decouple reference counting from page accounting Message-ID: <20200803150349.GA502356@cmpxchg.org> References: <20200623174037.3951353-1-guro@fb.com> <20200623174037.3951353-6-guro@fb.com> <20200803090033.GE5174@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200803090033.GE5174@dhcp22.suse.cz> X-Rspamd-Queue-Id: 4B3BC1A4CB X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Aug 03, 2020 at 11:00:33AM +0200, Michal Hocko wrote: > On Tue 23-06-20 10:40:23, Roman Gushchin wrote: > > @@ -5456,7 +5460,10 @@ static int mem_cgroup_move_account(struct page *page, > > */ > > smp_mb(); > > > > - page->mem_cgroup = to; /* caller should have done css_get */ > > + css_get(&to->css); > > + css_put(&from->css); > > + > > + page->mem_cgroup = to; > > > > __unlock_page_memcg(from); > > What prevents from memcg to be released here? ->attach_task() and kill_css() are exclusive through the cgroup_mutex, so the base ref cannot disappear from under us during this operation.