linux-kernel - Re: [syzbot] WARNING in follow_hugetlb

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Date:   Fri, 13 May 2022 15:48:15 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        syzbot <syzbot+acf65ca584991f3cc447@...kaller.appspotmail.com>,
        Minchan Kim <minchan@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        llvm@...ts.linux.dev, nathan@...nel.org, ndesaulniers@...gle.com,
        syzkaller-bugs@...glegroups.com, trix@...hat.com,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [syzbot] WARNING in follow_hugetlb_page

On 5/13/22 11:09, Mike Kravetz wrote:
> On 5/13/22 10:26, Andrew Morton wrote:
>> On Fri, 13 May 2022 09:43:24 -0700 syzbot <syzbot+acf65ca584991f3cc447@...kaller.appspotmail.com> wrote:
>>
>>> syzbot has found a reproducer for the following issue on:
>>
>> Thanks.
>>
>>> HEAD commit:    1e1b28b936ae Add linux-next specific files for 20220513
>>> git tree:       linux-next
>>> console+strace: https://syzkaller.appspot.com/x/log.txt?x=174ae715f00000
>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=e4eb3c0c4b289571
>>> dashboard link: https://syzkaller.appspot.com/bug?extid=acf65ca584991f3cc447
>>> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
>>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11531766f00000
>>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16ce5a9ef00000
>>>
>>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>>> Reported-by: syzbot+acf65ca584991f3cc447@...kaller.appspotmail.com
>>>
>>> ------------[ cut here ]------------
>>> WARNING: CPU: 1 PID: 3611 at mm/hugetlb.c:6250 follow_hugetlb_page+0x1326/0x1c80 mm/hugetlb.c:6250
>>
>> The try_grab_folio() added by 822951d84684d ("mm/hugetlb: Use
>> try_grab_folio() instead of try_grab_compound_head()").  That commit
>> has been there over a month so I guess it's something else.  Does
>> someone have the time to bisect?
> 
> I can recreate in my 'easy to debug' environment, so I can bisect in
> parallel with other things I need to do today.
> 

I isolated this to Minchan Kim's "mm: fix is_pinnable_page against on cma
page".  Yes, the fat finger fix is in next-20220513.

I don't have time to analyze right now, but can confirm that in the
reproducer is_pinnable_page is returning false after this change when it
previously returned true.
-- 
Mike Kravetz