linux-kernel - Re: [syzbot] BUG: unable to handle kernel paging request in alloc_huge

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Date:   Sat, 14 Aug 2021 15:06:52 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     syzbot <syzbot+57876cfc2dca0c6b2e6a@...kaller.appspotmail.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        mike.kravetz@...cle.com, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] BUG: unable to handle kernel paging request in
 alloc_huge_page

On Sat, 14 Aug 2021 04:07:23 -0700 syzbot <syzbot+57876cfc2dca0c6b2e6a@...kaller.appspotmail.com> wrote:

> Hello,
> 
> syzbot found the following issue on:

Thanks.

> HEAD commit:    92d00774360d Add linux-next specific files for 20210810
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=12e2b4d9300000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=a6933fa6f9a86ca9
> dashboard link: https://syzkaller.appspot.com/bug?extid=57876cfc2dca0c6b2e6a
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.1
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16f81581300000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11419dfa300000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+57876cfc2dca0c6b2e6a@...kaller.appspotmail.com
> 
> BUG: unable to handle page fault for address: fffffffffffffffc
> #PF: supervisor write access in kernel mode
> #PF: error_code(0x0002) - not-present page
> PGD b68f067 P4D b68f067 PUD b691067 PMD 0 
> Oops: 0002 [#1] PREEMPT SMP KASAN
> CPU: 0 PID: 6601 Comm: syz-executor361 Not tainted 5.14.0-rc5-next-20210810-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> RIP: 0010:__list_add include/linux/list.h:71 [inline]
> RIP: 0010:list_add include/linux/list.h:86 [inline]
> RIP: 0010:alloc_huge_page+0xdcb/0x11b0 mm/hugetlb.c:2821

That appears to be

		list_add(&page->lru, &h->hugepage_activelist);

I'm suspecting Mike's surplus page changes?

> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11419dfa300000

Nice to have that,