Re: [PATCH] uio/gen-pci: don't enable interrupts in ISR

Michael S. Tsirkin
2011-08-09T12:01:47Z

On Tue, Aug 09, 2011 at 01:43:46PM +0200, Sebastian Andrzej Siewior wrote:
> Michael S. Tsirkin wrote:
> >>It seems to me that you could drop this "user block" thing
> >>since you never change anything outside of this command register and it
> >>does not stop the race.
> >
> >I don't think so: if we did, we would lose userspace modifications to
> >other bits such as io enable, and there's no way to guess what their
> >values should be.
>
> How so?
>
> Sebastian

Let's assume we start with e.g. io enable bit cleared.

user kernel
read config |
set io enable |
| interrupt
| read + set interrupt mask
write config back |
write

We end up with io enable bit cleared. Locking around rmw
that we have fixes this race.

--
MST