On Tue, Sep 15, 2015 at 05:37:51PM -0700, K. Y. Srinivasan wrote:
> From: Olaf Hering <olaf@xxxxxxxxx>
>
> The callbacks in kvp, vss and fcopy code are called both from the main thread
> as well as from interrupt context. If a state change is done by the main
> thread it is not immediately seen by the interrupt. As a result the
> state machine gets out of sync.
>
> Force propagation of state changes via get/set helpers with a memory barrier.
>
> Signed-off-by: Olaf Hering <olaf@xxxxxxxxx>
> Signed-off-by: K. Y. Srinivasan <kys@xxxxxxxxxxxxx>
> ---
> drivers/hv/hyperv_vmbus.h | 14 ++++++++++++++
> 1 files changed, 14 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
> index 4b1eb6d..dee5798 100644
> --- a/drivers/hv/hyperv_vmbus.h
> +++ b/drivers/hv/hyperv_vmbus.h
> @@ -780,4 +780,18 @@ enum hvutil_device_state {
> HVUTIL_DEVICE_DYING, /* driver unload is in progress */
> };
>
> +static inline void hvutil_device_set_state(enum hvutil_device_state *p,
> + enum hvutil_device_state s)
> +{
> + *p = s;
> + wmb();
> +}
> +
> +static inline enum hvutil_device_state
> +hvutil_device_get_state(enum hvutil_device_state *p)
> +{
> + rmb();
> + return *p;
> +}
> +
> #endif /* _HYPERV_VMBUS_H */
This is crazy. If you need to know the state of something (pun
intended) then you had better be using a lock, and not relying on a
random pointer to contain a random value and be able to do something
based on that.
This shows the code is broken, don't paper over things by throwing in
random read/write barriers, that is a HUGE flag that something bad is
happening here.
Just use a lock, that's what it is there for.
greg k-h
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