Arm + KASAN + syzbot

[Arnd Bergmann]

On Thu, Mar 11, 2021 at 3:09 PM Russell King - ARM Linux admin
<linux at armlinux.org.uk> wrote:
> On Thu, Mar 11, 2021 at 02:55:54PM +0100, Linus Walleij wrote:
> > On Thu, Mar 11, 2021 at 11:54 AM Dmitry Vyukov <dvyukov at google.com> wrote:
> > > The instance has KASAN disabled because Go binaries don't run on KASAN kernel:
> > > https://lore.kernel.org/linux-arm-kernel/CACT4Y+YdJoNTqnBSELcEbcbVsKBtJfYUc7_GSXbUQfAJN3JyRg@mail.gmail.com/
> >
> > I am still puzzled by this, but I still have the open question about how much
> > memory the Go runtime really use. I am suspecting quite a lot, and the
> > ARM32 instance isn't on par with any contemporary server or desktop
> > when it comes to memory, it has ~2GB for a userspace program, after
> > that bad things will happen: the machine will start thrashing.
>
> I believe grafana is a Go binary - I run this in a VM with only 1G
> of memory and no swap along with apache. It's happy enough.
>
> USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
> grafana   1122  0.0  5.9 920344 60484 ?        Ssl  Feb18  28:31 /usr/sbin/grafana-server --config=/etc/grafana/grafana.ini ...
>
> So, I suspect it's basically KASAN upsetting Go somehow that then
> causes the memory usage to spiral out of control.

I found a bug report about someone complaining that Go reserves a lot of
virtual address space, and that this breaks an application that works
with VMSPLIT_3G
when changing to VMSPLIT_2G

https://github.com/golang/go/issues/35677

If KASAN limits the address space available to user space, there might be
a related issue, even when there is still physical memory available.

       Arnd