On Fri 28-08-20 12:07:55, Jan Kara wrote:
> On Wed 26-08-20 19:48:16, syzbot wrote:
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit: c3d8f220 Merge tag 'kbuild-fixes-v5.9' of git://git.kernel..
> > git tree: upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=15f83cb6900000
> > kernel config: https://syzkaller.appspot.com/x/.config?x=bb68b9e8a8cc842f
> > dashboard link: https://syzkaller.appspot.com/bug?extid=3622cea378100f45d59f
> > compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/
> > c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
> > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1287ac96900000
> > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11c7ac46900000
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+3622cea378100f45d...@syzkaller.appspotmail.com
> >
> > ------------[ cut here ]------------
> > kernel BUG at fs/ext4/inode.c:2598!
> > invalid opcode: 0000 [#1] PREEMPT SMP KASAN
> > CPU: 1 PID: 27612 Comm: syz-executor879 Not tainted 5.9.0-rc1-syzkaller #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> > Google 01/01/2011
> > RIP: 0010:mpage_prepare_extent_to_map+0xd34/0xd40 fs/ext4/inode.c:2598
>
> Doh, so this is:
>
> wait_on_page_writeback(page);
> >>> BUG_ON(PageWriteback(page));
>
> in mpage_prepare_extent_to_map(). So we have PageWriteback() page after we
> have called wait_on_page_writeback() on a locked page. Not sure how this
> could ever happen even less how ext4 could cause this...
I was poking a bit into this and there were actually recent changes into
page bit waiting logic by Linus. Linus, any idea?
Honza
--
Jan Kara <j...@suse.com>
SUSE Labs, CR
