Date: Fri, 05 Sep 2008 15:52:44 -0700 From: Julian Elischer <julian@elischer.org> To: FreeBSD Net <freebsd-net@freebsd.org> Subject: Re: rewrite of rt_check() (now rt_check_fib()) Message-ID: <48C1B83C.9000404@elischer.org> In-Reply-To: <48C1B774.2020405@elischer.org> References: <48C19568.807@elischer.org> <48C1B774.2020405@elischer.org>
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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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>
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