Serious bug in most (?) ethernet drivers (bge, bce, ixgb etc.).

[Vladimir Ivanov]

Bruce Evans wrote:

> On Thu, 5 Apr 2007, Vladimir Ivanov wrote:
>
>> We have reported serious bug with em driver 
>> (http://www.freebsd.org/cgi/query-pr.cgi?pr=kern/87418) one year and 
>> half ago.
>> It's very funny but most freebsd ethernet drivers cloned this bug I 
>> seem.
>> You can see same bug in bce, bge, ixgb and so on.
>
>
> I can only see it in bce and ixgb.  bge is much simpler and better --

Yes, you're right. I was too pessimistic. Thank you a lot.
I'll resend the bce patch to David.

> bge_rxeof() doesn't depend on any state after the unlock/re-lock except
> the rx indexes, and these are both reset to 0 by reinitialization.
>
> However, reinitialization often panics bge_rxeof() anyway.   The only
> reasons for the panics that I can think of is that nothing is declared
> volatile but the producer index is extremely volatile, so the following
> races are possible:
> - compiler caching the indexes.  bce implements this as foot-shooting.
>   I think aliasing problems prevent the compiler doing it, so declaring
>   things as volatile would make no difference.
> - a race with the hardware in initialzation might result in the producer
>   index being nonzero and for old data despite it having been reset to 0
>   and no new data arriving.  Stopping the hardware for initialization
>   should prevent such races.
>
> Bruce