From: "Paul E. McKenney" <paulmck@linux.ibm.com>
To: Herbert Xu <herbert@gondor.apana.org.au>
Cc: NeilBrown <neilb@suse.com>, Thomas Graf <tgraf@suug.ch>,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/4] rhashtable: use bit_spin_locks to protect hash bucket.
Date: Tue, 26 Mar 2019 08:36:46 -0700 [thread overview]
Message-ID: <20190326153646.GL4102@linux.ibm.com> (raw)
In-Reply-To: <20190326050320.gwk3tgtqwl5csivt@gondor.apana.org.au>
On Tue, Mar 26, 2019 at 01:03:20PM +0800, Herbert Xu wrote:
> On Mon, Mar 25, 2019 at 04:05:39PM +1100, NeilBrown wrote:
> >
> > + * Sometimes we unlock a bucket by writing a new pointer there. In that
> > + * case we don't need to unlock, but we do need to reset state such as
> > + * local_bh. For that we have rht_unlocked(). This doesn't include
> > + * the memory barrier that bit_spin_unlock() provides, but rcu_assign_pointer()
> > + * will have provided that.
>
> Hmm, are you sure that's enough? IIRC rcu_assign_pointer only
> provides a write barrier compared to the more complete (but one-way)
> barrier that a spin-lock provides.
Not seeing the code, I have no opinion on the safety in this case,
but I did want to mention that rcu_assign_pointer() has been upgraded
to a release store, so that it orders all prior accesses from the
viewpoint of some other thread that just picked up the stored pointer
via rcu_dereference().
But you are quite right, rcu_assign_pointer() used to just do an
smp_wmb(). It is now new and improved! ;-)
Thanx, Paul
next prev parent reply other threads:[~2019-03-26 15:36 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-25 5:05 [PATCH 0/4] Convert rhashtable to use bitlocks NeilBrown
2019-03-25 5:05 ` [PATCH 1/4] rhashtable: use cmpxchg() in nested_table_alloc() NeilBrown
2019-03-25 5:05 ` [PATCH 3/4] rhashtable: use bit_spin_locks to protect hash bucket NeilBrown
2019-03-26 5:03 ` Herbert Xu
2019-03-26 15:36 ` Paul E. McKenney [this message]
2019-03-27 3:45 ` Herbert Xu
2019-03-26 22:35 ` NeilBrown
2019-03-27 3:45 ` Herbert Xu
2019-03-27 15:04 ` Paul E. McKenney
2019-03-26 5:27 ` Herbert Xu
2019-03-26 22:40 ` NeilBrown
2019-03-25 5:05 ` [PATCH 4/4] rhashtable: add lockdep tracking to bucket bit-spin-locks NeilBrown
2019-03-25 5:05 ` [PATCH 2/4] rhashtable: allow rht_bucket_var to return NULL NeilBrown
-- strict thread matches above, loose matches on Subject: below --
2019-04-01 23:07 [PATCH 0/4 v2] Convert rhashtable to use bitlocks NeilBrown
2019-04-01 23:07 ` [PATCH 3/4] rhashtable: use bit_spin_locks to protect hash bucket NeilBrown
2019-04-02 10:11 ` David Laight
2019-04-02 21:10 ` NeilBrown
2019-04-03 9:26 ` David Laight
2019-04-04 0:13 ` NeilBrown
2019-04-08 2:34 ` Herbert Xu
2019-04-10 19:34 ` Guenter Roeck
2019-04-11 0:48 ` NeilBrown
2019-04-11 2:15 ` David Miller
2019-04-11 6:13 ` NeilBrown
2019-04-11 6:40 ` NeilBrown
2019-04-11 12:44 ` Guenter Roeck
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