rewrite of rt_check() (now rt_check_fib())

[Julian Elischer]

Julian Elischer wrote:
> Julian Elischer wrote:
>> In tryin gto understand rt_check_fib() (wsa rt_check()) I ended up 
>> rewriting it to do what I thought it was trying to do..
>> this stops the panics some people have seen, but allows the system to 
>> stay up long enough to see some other problem..
>> anyhow this si the patch:
>>
>> comments?
>>
> 
> I was thinking about this a bit.
> 
> rt_check_fib() drops the lock on the given rtentry in order to be able 
> to get a lock on another rtentry that MIGHT be the same rtentry.
> 
> while it is doing this, another processor could free the original 
> rtentry. The only safw way to get around this is to hold an additional 
> reference on the first rtentry (we don't already have one) while it is 
> unlocked so that we can be sure that it is not actually freed if this 
> happens.
> 
> to do this safely I'd have to add a couple of new items into route.h:
> 
> #define RT_TEMP_UNLOCK(_rt) do {                                \
>         RT_ADDREF(_rt);                                         \
>         RT_UNLOCK(_rt);                                         \
> } while (0)
> 
> #define RT_RELOCK(_rt) do {                                     \
>         RT_LOCK(_rt)                                            \
>         if ((_rt)->rt_refcnt <= 1)                              \
>                 rtfree(_rt);                                    \
>                 _rt = 0; /*  signal that it went away */        \
>         else {                                                  \
>                 RT_REMREF(_rt);                                 \
>                 RT_UNLOCK(_rt);   

duh remove that line!

                               \
>                 /* note that _rt is still valid */              \
>         }                                                       \
> } while (0)
> 
> 
> the new version of rt_check is attached.....
> 
> 
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