Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   sunqiuyang <sunqiuyang@huawei.com>
To:     Michal Hocko <mhocko@kernel.org>
CC:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>
Subject: RE: [PATCH 1/1] mm/migrate: fix list corruption in migration of
 non-LRU movable pages
Thread-Topic: [PATCH 1/1] mm/migrate: fix list corruption in migration of
 non-LRU movable pages
Thread-Index: AQHVYi7CKRiSaGuZ20KJAhdeZXNZ4qcZaW+AgAFf/lT//8LbAIAAjGWd//+OTACAAMgqDv//hZcAACt21AY=
Date:   Thu, 5 Sep 2019 01:44:12 +0000
Message-ID: <157FC541501A9C4C862B2F16FFE316DC190C5990@dggeml512-mbx.china.huawei.com>
References: <20190903082746.20736-1-sunqiuyang@huawei.com>
 <20190903131737.GB18939@dhcp22.suse.cz>
 <157FC541501A9C4C862B2F16FFE316DC190C1B09@dggeml512-mbx.china.huawei.com>
 <20190904063836.GD3838@dhcp22.suse.cz>
 <157FC541501A9C4C862B2F16FFE316DC190C2EBD@dggeml512-mbx.china.huawei.com>
 <20190904081408.GF3838@dhcp22.suse.cz>
 <157FC541501A9C4C862B2F16FFE316DC190C3402@dggeml512-mbx.china.huawei.com>,<20190904125226.GV3838@dhcp22.suse.cz>
In-Reply-To: <20190904125226.GV3838@dhcp22.suse.cz>
Accept-Language: en-US, zh-CN
Content-Language: en-US
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 8BIT
MIME-Version: 1.0
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


________________________________________
From: Michal Hocko [mhocko@kernel.org]
Sent: Wednesday, September 04, 2019 20:52
To: sunqiuyang
Cc: linux-kernel@vger.kernel.org; linux-mm@kvack.org
Subject: Re: [PATCH 1/1] mm/migrate: fix list corruption in migration of non-LRU movable pages

On Wed 04-09-19 12:19:11, sunqiuyang wrote:
> > Do not top post please
> >
> > On Wed 04-09-19 07:27:25, sunqiuyang wrote:
> > > isolate_migratepages_block() from another thread may try to isolate the page again:
> > >
> > > for (; low_pfn < end_pfn; low_pfn++) {
> > >   /* ... */
> > >   page = pfn_to_page(low_pfn);
> > >  /* ... */
> > >   if (!PageLRU(page)) {
> > >     if (unlikely(__PageMovable(page)) && !PageIsolated(page)) {
> > >         /* ... */
> > >         if (!isolate_movable_page(page, isolate_mode))
> > >           goto isolate_success;
> > >       /*... */
> > > isolate_success:
> > >      list_add(&page->lru, &cc->migratepages);
> > >
> > > And this page will be added to another list.
> > > Or, do you see any reason that the page cannot go through this path?
> >
> > The page shouldn't be __PageMovable after the migration is done. All the
> > state should have been transfered to the new page IIUC.
> >
>
> I don't see where page->mapping is modified after the migration is done.
>
> Actually, the last comment in move_to_new_page() says,
> "Anonymous and movable page->mapping will be cleard by
> free_pages_prepare so don't reset it here for keeping
> the type to work PageAnon, for example. "
>
> Or did I miss something? Thanks,

This talks about mapping rather than flags stored in the mapping.
I can see that in tree migration handlers (z3fold_page_migrate,
vmballoon_migratepage via balloon_page_delete, zs_page_migrate via
reset_page) all reset the movable flag. I am not sure whether that is a
documented requirement or just a coincidence. Maybe it should be
documented. I would like to hear from Minchan.

---
I checked the three migration handlers and only found __ClearPageMovable,
which clears registered address_space val with keeping PAGE_MAPPING_MOVABLE flag,
so the page should still be __PageMovable when caught by another migration thread. Right?

---

--
Michal Hocko
SUSE Labs