linux-kernel - RE: [PATCH v1] mm: migration: fix the FOLL

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Message-ID: <BYAPR11MB3495AC9B3F989A3462053C24F7699@BYAPR11MB3495.namprd11.prod.outlook.com>
Date:   Sun, 14 Aug 2022 06:49:24 +0000
From:   "Wang, Haiyue" <haiyue.wang@...el.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
CC:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "david@...hat.com" <david@...hat.com>,
        "linmiaohe@...wei.com" <linmiaohe@...wei.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        "songmuchun@...edance.com" <songmuchun@...edance.com>,
        "naoya.horiguchi@...ux.dev" <naoya.horiguchi@...ux.dev>
Subject: RE: [PATCH v1] mm: migration: fix the FOLL_GET failure on following
 huge page

> -----Original Message-----
> From: Wang, Haiyue
> Sent: Sunday, August 14, 2022 14:20
> To: Andrew Morton <akpm@...ux-foundation.org>
> Cc: linux-mm@...ck.org; linux-kernel@...r.kernel.org; david@...hat.com; linmiaohe@...wei.com; Huang,
> Ying <ying.huang@...el.com>; songmuchun@...edance.com; naoya.horiguchi@...ux.dev
> Subject: RE: [PATCH v1] mm: migration: fix the FOLL_GET failure on following huge page
> 
> > -----Original Message-----
> > From: Andrew Morton <akpm@...ux-foundation.org>
> > Sent: Sunday, August 14, 2022 07:29
> > To: Wang, Haiyue <haiyue.wang@...el.com>
> > Cc: linux-mm@...ck.org; linux-kernel@...r.kernel.org; david@...hat.com; linmiaohe@...wei.com; Huang,
> > Ying <ying.huang@...el.com>; songmuchun@...edance.com; naoya.horiguchi@...ux.dev
> > Subject: Re: [PATCH v1] mm: migration: fix the FOLL_GET failure on following huge page
> >
> > On Fri, 12 Aug 2022 16:49:21 +0800 Haiyue Wang <haiyue.wang@...el.com> wrote:
> >
> > > Not all huge page APIs support FOLL_GET option, so the __NR_move_pages
> > > will fail to get the page node information for huge page.
> >


> > Is a -stable backport warranted?
> 
> Yes.
> 
> Since the mainline has introduced the new patch:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=3218f8712d6bb
> 

Looks like 'is_zone_device_page' will cause 'FOLL_GET' page reference count issue, which should
call 'put_page' before call branch jump.

try_grab_page --> 
		if (flags & FOLL_GET)
			folio_ref_inc(folio);

Or I misunderstood the 'is_zone_device_page' ? ;-)

> The backported needs to rebase like for 5.19:
> 
> -		if (page && !is_zone_device_page(page)) {
> +		if (page) {
> 
> >
> > >