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From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Wed, 26 Oct 2022 06:25:27 -0700
Message-ID: <CACT4Y+YTjYMWQKixhkNMuty4LXTsgBmpiYAN5ChGVXZBCyp0uA@mail.gmail.com>
Subject: Re: [syzbot] WARNING in __split_huge_page_tail
To:     David Hildenbrand <david@redhat.com>
Cc:     syzbot <syzbot+273b547b15eb58ea35e8@syzkaller.appspotmail.com>,
        akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, syzkaller-bugs@googlegroups.com
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On Wed, 26 Oct 2022 at 02:54, David Hildenbrand <david@redhat.com> wrote:
>
> On 26.10.22 08:59, syzbot wrote:
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit:    4da34b7d175d Merge tag 'thermal-6.1-rc2' of git://git.kern..
> > git tree:       upstream
> > console+strace: https://syzkaller.appspot.com/x/log.txt?x=113bd8bc880000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=4789759e8a6d5f57
> > dashboard link: https://syzkaller.appspot.com/bug?extid=273b547b15eb58ea35e8
> > compiler:       Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=161e1f62880000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16dd4fe6880000
> >
> > Downloadable assets:
> > disk image: https://storage.googleapis.com/syzbot-assets/a61ddb36c296/disk-4da34b7d.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/ceee41246252/vmlinux-4da34b7d.xz
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+273b547b15eb58ea35e8@syzkaller.appspotmail.com
> >
> >   tlb_finish_mmu+0xcb/0x200 mm/mmu_gather.c:363
> >   exit_mmap+0x2b1/0x670 mm/mmap.c:3098
> >   __mmput+0x114/0x3b0 kernel/fork.c:1185
> >   exit_mm+0x217/0x2f0 kernel/exit.c:516
> >   do_exit+0x5e7/0x2070 kernel/exit.c:807
> >   do_group_exit+0x1fd/0x2b0 kernel/exit.c:950
> >   __do_sys_exit_group kernel/exit.c:961 [inline]
> >   __se_sys_exit_group kernel/exit.c:959 [inline]
> >   __x64_sys_exit_group+0x3b/0x40 kernel/exit.c:959
> >   do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> >   do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
> >   entry_SYSCALL_64_after_hwframe+0x63/0xcd
> > ------------[ cut here ]------------
> > WARNING: CPU: 0 PID: 3908 at mm/huge_memory.c:2465 __split_huge_page_tail+0x81c/0x1080 mm/huge_memory.c:2465
>
> Is this the
>
> VM_BUG_ON_PAGE(atomic_read(&page_tail->_mapcount) != -1, page_tail);
>
> assertion?

Hi David,

You can check the sources for that revision, but on the dashboard
there are clickable links for all source references:
https://syzkaller.appspot.com/bug?extid=273b547b15eb58ea35e8

In this case it points to:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/mm/huge_memory.c?id=4da34b7d175dc99b8befebd69e96546c960d526c#n2465