On Fri, Sep 30, 2005 at 11:56:41PM -0700, Suzanne Wood wrote:
>
> But it is interesting to have discarded what was developed yesterday
> to minimize rcu_dereference impact:
>
> >> ----- Original message -----
> >> From: Herbert Xu <[email protected]>
> >> Date: Fri, 30 Sep 2005 11:19:07 +1000
> >>
> >> On Thu, Sep 29, 2005 at 06:16:03PM -0700, Paul E. McKenney wrote:
> >>>
> >>> OK, how about this instead?
> >>>
> >>> rcu_read_lock();
> >>> in_dev = dev->ip_ptr;
> >>> if (in_dev) {
> >>> atomic_inc(&rcu_dereference(in_dev)->refcnt);
> >>> }
> >>> rcu_read_unlock();
> >>> return in_dev;
> >>
> >> Looks great.
>
> while adding a function call level by wrapping __in_dev_get_rcu
> with in_dev_get as suggested here.
It might look different, but it should compile to the same result.
GCC should be smart enough to combine the two branches and produce a
memory barrier only when in_dev is not NULL.
> The other thing I'd hoped to address in pktgen.c was
> removing the __in_dev_put() which decrements refcnt
> while __in_dev_get_rcu() does not increment.
Well spotted.
Here is a patch on top of the last one to fix this bogus decrement.
Signed-off-by: Herbert Xu <[email protected]>
Thanks,
--
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <[email protected]>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
diff --git a/net/core/pktgen.c b/net/core/pktgen.c
--- a/net/core/pktgen.c
+++ b/net/core/pktgen.c
@@ -1673,7 +1673,6 @@ static void pktgen_setup_inject(struct p
pkt_dev->saddr_min = in_dev->ifa_list->ifa_address;
pkt_dev->saddr_max = pkt_dev->saddr_min;
}
- __in_dev_put(in_dev);
}
rcu_read_unlock();
}
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