[PATCH 1/1] staging: hv: Fix race condition on IC channel initialization
Greg KH
gregkh at suse.de
Fri May 21 22:22:01 UTC 2010
On Fri, May 21, 2010 at 10:07:17PM +0000, Haiyang Zhang wrote:
> > From: Greg KH [mailto:gregkh at suse.de]
> > > +/* Counter of IC channels initialized */
> > > +atomic_t hv_utils_initcnt = ATOMIC_INIT(0);
> >
> > This doesn't need to be an atomic variable, does it really?
> >
> > Why not have a simple bool variable "vmbus_initialized" or something.
> > It starts out as false, and then turns true when you are up and ready.
> > Then provide a function that tests it:
> > bool hv_vmbus_ready(void)
> > {
> > return vmbus_initialized
> > }
> > EXPORT_SYMBOL_GPL(hv_vmbus_ready);
> >
> >
> > this turns into a simple function call, again, never needing to know
> > about message types or any other mess.
>
> This looks good. I will add the hv_vmbus_ready() function. It doesn't even
> have to be exported symbol, because it's only used in vmbus module to ensure
> all channels are ready before vmbus_init() returns. Other modules won't get a
> chance to see uninitialized channels after hv_vmbus is loaded.
>
> Also, I'll cleanup the printk in hv_utils load/unload.
>
> Regarding the atomic variable -- the channel offer processing function is
> triggered by interrupts from host -- should we be concerned about "counter++"
> racing with each other in two interrupts happening around the same time?
If you are, having races like this, then you should be using a lock to
protect lots of things, not just one single atomic variable, right?
thanks,
greg k-h
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