[PATCH/RFC] net: Add __napi_sycnhronize() to sync with napi poll

[Jeff Garzik]

Benjamin Herrenschmidt wrote:
> net: Add __napi_synchronize() to sync with napi poll
> 
> The EMAC driver which needs to handle multiple devices with one
> NAPI instance implements its own per-channel disable bit. However,
> when setting such a bit, it needs to synchronize with the poller
> (that is make sure that any pending poller instance has completed,
> or is started late enough to see that disable bit).
> 
> This implements a low level __napi_synchronize() function to acheive
> that. The underscores are to emphasis the low level aspect of it and
> to discourage driver writers who don't know what they are doing to
> use it (to please DaveM :-)
> 
> Signed-off-by: Benjamin Herrenschmidt <benh at kernel.crashing.org>
> ---
> 
> Switched to do a cpu_relax() spin instead and only on SMP. Not that
> we have an smp_mb() in there which synchronize_irq() lacks. I believe
> this is a bug in synchronize_irq() which I'll handle separately.
> 
> Note: unfortunately, Jeff already picked up the EMAC patch without
> waiting for this to be sorted out (oops...). So if you agree with
> this patch, it would be nice to have it go in quickly or maybe via
> Jeff's tree to avoid breakage ? Not terribly important tho.


Sorry, I thought that was the way everybody was headed.  With the driver 
broken /anyway/, I just sorta threw it into the pile of fixes.

It's upstream now, so let me know if you want to revert or move forward 
from here...

	Jeff