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Mon, 16 Mar 2020 07:58:26 -0700 (PDT) Date: Mon, 16 Mar 2020 15:58:25 +0100 From: Michal Hocko To: Chris Down Cc: Andrew Morton , Johannes Weiner , Tejun Heo , Roman Gushchin , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: Re: [PATCH 4/6] mm, memcg: Prevent memory.min load/store tearing Message-ID: <20200316145825.GP11482@dhcp22.suse.cz> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Thu 12-03-20 17:33:07, Chris Down wrote: > This can be set concurrently with reads, which may cause the wrong value > to be propagated. > > Signed-off-by: Chris Down > Cc: Andrew Morton > Cc: Johannes Weiner > Cc: Roman Gushchin > Cc: Tejun Heo > Cc: linux-mm@kvack.org > Cc: cgroups@vger.kernel.org > Cc: linux-kernel@vger.kernel.org > Cc: kernel-team@fb.com Acked-by: Michal Hocko > --- > mm/memcontrol.c | 4 ++-- > mm/page_counter.c | 10 ++++++---- > 2 files changed, 8 insertions(+), 6 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index c85a304fa4a1..e0ed790a2a8c 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -6261,7 +6261,7 @@ enum mem_cgroup_protection mem_cgroup_protected(struct mem_cgroup *root, > if (!usage) > return MEMCG_PROT_NONE; > > - emin = memcg->memory.min; > + emin = READ_ONCE(memcg->memory.min); > elow = READ_ONCE(memcg->memory.low); > > parent = parent_mem_cgroup(memcg); > @@ -6277,7 +6277,7 @@ enum mem_cgroup_protection mem_cgroup_protected(struct mem_cgroup *root, > if (emin && parent_emin) { > unsigned long min_usage, siblings_min_usage; > > - min_usage = min(usage, memcg->memory.min); > + min_usage = min(usage, READ_ONCE(memcg->memory.min)); > siblings_min_usage = atomic_long_read( > &parent->memory.children_min_usage); > > diff --git a/mm/page_counter.c b/mm/page_counter.c > index 18b7f779f2e2..ae471c7d255f 100644 > --- a/mm/page_counter.c > +++ b/mm/page_counter.c > @@ -17,14 +17,16 @@ static void propagate_protected_usage(struct page_counter *c, > unsigned long usage) > { > unsigned long protected, old_protected; > - unsigned long low; > + unsigned long low, min; > long delta; > > if (!c->parent) > return; > > - if (c->min || atomic_long_read(&c->min_usage)) { > - if (usage <= c->min) > + min = READ_ONCE(c->min); > + > + if (min || atomic_long_read(&c->min_usage)) { > + if (usage <= min) > protected = usage; > else > protected = 0; > @@ -217,7 +219,7 @@ void page_counter_set_min(struct page_counter *counter, unsigned long nr_pages) > { > struct page_counter *c; > > - counter->min = nr_pages; > + WRITE_ONCE(counter->min, nr_pages); > > for (c = counter; c; c = c->parent) > propagate_protected_usage(c, atomic_long_read(&c->usage)); > -- > 2.25.1 > -- Michal Hocko SUSE Labs