On Thu, Feb 21, 2019 at 11:36:24AM -0800, Andrew Morton wrote: > On Thu, 21 Feb 2019 06:52:04 -0800 syzbot <syzbot+ca95b2b7aef9e7cbd6ab@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > > Hello, > > > > syzbot found the following crash on: > > > > HEAD commit: 4aa9fc2a435a Revert "mm, memory_hotplug: initialize struct.. > > git tree: upstream > > console output: https://syzkaller.appspot.com/x/log.txt?x=1101382f400000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=4fceea9e2d99ac20 > > dashboard link: https://syzkaller.appspot.com/bug?extid=ca95b2b7aef9e7cbd6ab > > compiler: gcc (GCC) 9.0.0 20181231 (experimental) > > > > Unfortunately, I don't have any reproducer for this crash yet. > > Not understanding. That seems to be saying that we got a NULL pointer > deref in __generic_file_write_iter() at > > written = generic_perform_write(file, from, iocb->ki_pos); > > which isn't possible. > > I'm not seeing recent changes in there which could have caused this. Help. FWIW, the panic happened in generic_perform_write() when it called a_ops->write_begin, which was NULL. I agree with Jann that the unwinders should handle this scenario better. -- Josh
