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Fri, 03 Jan 2020 11:29:07 -0800 (PST) Received: from [2620:15c:17:3:3a5:23a7:5e32:4598] ([2620:15c:17:3:3a5:23a7:5e32:4598]) by smtp.gmail.com with ESMTPSA id u23sm68353574pfm.29.2020.01.03.11.29.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 03 Jan 2020 11:29:06 -0800 (PST) Date: Fri, 3 Jan 2020 11:29:06 -0800 (PST) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Wei Yang cc: hannes@cmpxchg.org, mhocko@kernel.org, vdavydov.dev@gmail.com, akpm@linux-foundation.org, kirill.shutemov@linux.intel.com, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, yang.shi@linux.alibaba.com Subject: Re: [RFC PATCH] mm: thp: grab the lock before manipulation defer list In-Reply-To: <20200103143407.1089-1-richardw.yang@linux.intel.com> Message-ID: References: <20200103143407.1089-1-richardw.yang@linux.intel.com> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII 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 Fri, 3 Jan 2020, Wei Yang wrote: > As all the other places, we grab the lock before manipulate the defer list. > Current implementation may face a race condition. > > Fixes: 87eaceb3faa5 ("mm: thp: make deferred split shrinker memcg aware") > > Signed-off-by: Wei Yang > > --- > I notice the difference during code reading and just confused about the > difference. No specific test is done since limited knowledge about cgroup. > > Maybe I miss something important? The check for !list_empty(page_deferred_list(page)) must certainly be serialized with doing list_del_init(page_deferred_list(page)). > --- > mm/memcontrol.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index bc01423277c5..62b7ec34ef1a 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -5368,12 +5368,12 @@ static int mem_cgroup_move_account(struct page *page, > } > > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > + spin_lock(&from->deferred_split_queue.split_queue_lock); > if (compound && !list_empty(page_deferred_list(page))) { > - spin_lock(&from->deferred_split_queue.split_queue_lock); > list_del_init(page_deferred_list(page)); > from->deferred_split_queue.split_queue_len--; > - spin_unlock(&from->deferred_split_queue.split_queue_lock); > } > + spin_unlock(&from->deferred_split_queue.split_queue_lock); > #endif > /* > * It is safe to change page->mem_cgroup here because the page > @@ -5385,13 +5385,13 @@ static int mem_cgroup_move_account(struct page *page, > page->mem_cgroup = to; > > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > + spin_lock(&to->deferred_split_queue.split_queue_lock); > if (compound && list_empty(page_deferred_list(page))) { > - spin_lock(&to->deferred_split_queue.split_queue_lock); > list_add_tail(page_deferred_list(page), > &to->deferred_split_queue.split_queue); > to->deferred_split_queue.split_queue_len++; > - spin_unlock(&to->deferred_split_queue.split_queue_lock); > } > + spin_unlock(&to->deferred_split_queue.split_queue_lock); > #endif > > spin_unlock_irqrestore(&from->move_lock, flags); > -- > 2.17.1 > > >