From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wei Yang Subject: Re: [RFC PATCH] mm: thp: grab the lock before manipulation defer list Date: Tue, 7 Jan 2020 09:22:41 +0800 Message-ID: <20200107012241.GA15341@richard> References: <20200103143407.1089-1-richardw.yang@linux.intel.com> <20200106102345.GE12699@dhcp22.suse.cz> Reply-To: Wei Yang Mime-Version: 1.0 Return-path: Content-Disposition: inline In-Reply-To: <20200106102345.GE12699@dhcp22.suse.cz> Sender: linux-kernel-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Michal Hocko Cc: Wei Yang , 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 On Mon, Jan 06, 2020 at 11:23:45AM +0100, Michal Hocko wrote: >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? > Hmm... access the list without proper lock leads to many bad behaviors. For example, if we grab the lock after checking list_empty, the page may already be removed from list in split_huge_page_list. And then list_del_init would trigger bug. -- Wei Yang Help you, Help me