From: "Paul E. McKenney" <paulmck@us.ibm.com>
To: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Suzanne Wood <suzannew@cs.pdx.edu>,
Robert.Olsson@data.slu.se, davem@davemloft.net,
linux-kernel@vger.kernel.org, netdev@oss.sgi.com,
walpole@cs.pdx.edu
Subject: Re: [RFC][PATCH] identify in_dev_get rcu read-side critical sections
Date: Sat, 1 Oct 2005 11:04:41 -0700 [thread overview]
Message-ID: <20051001180441.GA1578@us.ibm.com> (raw)
In-Reply-To: <20051001071248.GA15990@gondor.apana.org.au>
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:
> >
> > But it is interesting to have discarded what was developed yesterday
> > to minimize rcu_dereference impact:
> >
> > >> ----- 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:
> > >>>
> > >>> 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.
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~} <herbert@gondor.apana.org.au>
> 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();
> }
next prev parent reply other threads:[~2005-10-01 18:03 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-10-01 6:56 [RFC][PATCH] identify in_dev_get rcu read-side critical sections Suzanne Wood
2005-10-01 7:12 ` Herbert Xu
2005-10-01 18:04 ` Paul E. McKenney [this message]
-- strict thread matches above, loose matches on Subject: below --
2005-10-01 18:37 Suzanne Wood
2005-10-01 19:29 ` Herbert Xu
2005-10-01 18:00 Suzanne Wood
2005-09-30 1:06 Suzanne Wood
2005-10-01 1:13 ` Herbert Xu
2005-09-29 23:59 Suzanne Wood
2005-09-30 0:23 ` Herbert Xu
2005-09-29 23:39 Suzanne Wood
2005-09-29 23:30 Suzanne Wood
2005-09-30 0:21 ` Herbert Xu
2005-09-30 0:23 ` Paul E. McKenney
2005-09-30 0:27 ` Herbert Xu
2005-09-30 0:36 ` Paul E. McKenney
2005-09-30 1:04 ` Herbert Xu
2005-09-30 1:16 ` Paul E. McKenney
2005-09-30 1:19 ` Herbert Xu
2005-09-29 16:02 Suzanne Wood
2005-09-29 21:28 ` Herbert Xu
2005-09-28 0:22 Suzanne Wood
2005-09-08 17:12 Suzanne Wood
2005-09-27 20:56 ` David S. Miller
2005-09-28 2:55 ` Herbert Xu
2005-09-28 14:51 ` Paul E. McKenney
2005-09-28 22:11 ` Herbert Xu
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