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[213.151.95.130]) by smtp.gmail.com with ESMTPSA id u1sm22257183wmc.5.2020.01.06.02.23.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 06 Jan 2020 02:23:46 -0800 (PST) Date: Mon, 6 Jan 2020 11:23:45 +0100 From: Michal Hocko To: Wei Yang Cc: hannes@cmpxchg.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 Message-ID: <20200106102345.GE12699@dhcp22.suse.cz> References: <20200103143407.1089-1-richardw.yang@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200103143407.1089-1-richardw.yang@linux.intel.com> User-Agent: Mutt/1.12.2 (2019-09-21) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 03-01-20 22:34:07, Wei Yang wrote: > As all the other places, we grab the lock before manipulate the defer list. > Current implementation may face a race condition. Please always make sure to describe the effect of the change. Why a racy list_empty check matters? > 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? > --- > 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 -- Michal Hocko SUSE Labs