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

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


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