Re: [RFC][PATCH] identify in_dev_get rcu read-side critical sections
From: Paul E. McKenney <hidden>
Date: 2005-10-01 18:04:41
On Sat, Oct 01, 2005 at 05:12:48PM +1000, Herbert Xu wrote:
On Fri, Sep 30, 2005 at 11:56:41PM -0700, Suzanne Wood wrote:quoted
But it is interesting to have discarded what was developed yesterday to minimize rcu_dereference impact:quoted
quoted
----- Original message ----- From: Herbert Xu <herbert@gondor.apana.org.au> Date: Fri, 30 Sep 2005 11:19:07 +1000 On Thu, Sep 29, 2005 at 06:16:03PM -0700, Paul E. McKenney wrote:quoted
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.quoted
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.
Both this and Herbert's prior patch look good to me! Thanx, Paul
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au> Thanks, -- Visit Openswan at http://www.openswan.org/ Email: Herbert Xu ~{PmV>HI~} [off-list ref] Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
quoted hunk
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(); }