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Mon, 16 Mar 2020 07:57:41 -0700 (PDT) Date: Mon, 16 Mar 2020 15:57:40 +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 3/6] mm, memcg: Prevent memory.low load/store tearing Message-ID: <20200316145740.GO11482@dhcp22.suse.cz> References: <448206f44b0fa7be9dad2ca2601d2bcb2c0b7844.1584034301.git.chris@chrisdown.name> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <448206f44b0fa7be9dad2ca2601d2bcb2c0b7844.1584034301.git.chris@chrisdown.name> 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 17:33:01, 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 | 9 ++++++--- > 2 files changed, 8 insertions(+), 5 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index aca2964ea494..c85a304fa4a1 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -6262,7 +6262,7 @@ enum mem_cgroup_protection mem_cgroup_protected(struct mem_cgroup *root, > return MEMCG_PROT_NONE; > > emin = memcg->memory.min; > - elow = memcg->memory.low; > + elow = READ_ONCE(memcg->memory.low); > > parent = parent_mem_cgroup(memcg); > /* No parent means a non-hierarchical mode on v1 memcg */ > @@ -6291,7 +6291,7 @@ enum mem_cgroup_protection mem_cgroup_protected(struct mem_cgroup *root, > if (elow && parent_elow) { > unsigned long low_usage, siblings_low_usage; > > - low_usage = min(usage, memcg->memory.low); > + low_usage = min(usage, READ_ONCE(memcg->memory.low)); > siblings_low_usage = atomic_long_read( > &parent->memory.children_low_usage); > > diff --git a/mm/page_counter.c b/mm/page_counter.c > index 50184929b61f..18b7f779f2e2 100644 > --- a/mm/page_counter.c > +++ b/mm/page_counter.c > @@ -17,6 +17,7 @@ static void propagate_protected_usage(struct page_counter *c, > unsigned long usage) > { > unsigned long protected, old_protected; > + unsigned long low; > long delta; > > if (!c->parent) > @@ -34,8 +35,10 @@ static void propagate_protected_usage(struct page_counter *c, > atomic_long_add(delta, &c->parent->children_min_usage); > } > > - if (c->low || atomic_long_read(&c->low_usage)) { > - if (usage <= c->low) > + low = READ_ONCE(c->low); > + > + if (low || atomic_long_read(&c->low_usage)) { > + if (usage <= low) > protected = usage; > else > protected = 0; > @@ -231,7 +234,7 @@ void page_counter_set_low(struct page_counter *counter, unsigned long nr_pages) > { > struct page_counter *c; > > - counter->low = nr_pages; > + WRITE_ONCE(counter->low, 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