linux-kernel - Re: [PATCH] mm/gup: Add folio to list when folio_isolate

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Date:   Thu, 2 Feb 2023 02:13:55 +0000
From:   Kuan-Ying Lee (李冠穎) 
        <Kuan-Ying.Lee@...iatek.com>
To:     "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
CC:     Andrew Yang (楊智強) 
        <Andrew.Yang@...iatek.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Chinwen Chang (張錦文) 
        <chinwen.chang@...iatek.com>,
        "apopple@...dia.com" <apopple@...dia.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "jhubbard@...dia.com" <jhubbard@...dia.com>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>
Subject: Re: [PATCH] mm/gup: Add folio to list when folio_isolate_lru()
 succeed

On Tue, 2023-01-31 at 15:17 -0800, Andrew Morton wrote:
> On Tue, 31 Jan 2023 14:32:06 +0800 Kuan-Ying Lee <
> Kuan-Ying.Lee@...iatek.com> wrote:
> 
> > If we call folio_isolate_lru() successfully, we will get
> > return value 0. We need to add this folio to the
> > movable_pages_list.
> > 
> > Fixes: 67e139b02d99 ("mm/gup.c: refactor
> > check_and_migrate_movable_pages()")
> > Signed-off-by: Kuan-Ying Lee <Kuan-Ying.Lee@...iatek.com>
> > 
> > ...
> > 
> > --- a/mm/gup.c
> > +++ b/mm/gup.c
> > @@ -1914,7 +1914,7 @@ static unsigned long
> > collect_longterm_unpinnable_pages(
> >  			drain_allow = false;
> >  		}
> >  
> > -		if (!folio_isolate_lru(folio))
> > +		if (folio_isolate_lru(folio))
> >  			continue;
> >  
> >  		list_add_tail(&folio->lru, movable_page_list);
> 
> Thanks.  What are the user-visible effects of this bug?

Hi Andrew,

I didn't hit bug on real devices. I observe this issue
by tracing get_user_pages() call flow.

Thanks.