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+3622cea378100f45d59f@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > ------------[ 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 <jack@xxxxxxxx> SUSE Labs, CR
