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From: Herbert Xu <herbert@gondor.apana.org.au>
To: NeilBrown <neilb@suse.com>
Cc: Thomas Graf <tgraf@suug.ch>,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 08/18] rhashtable: clean up dereference of ->future_tbl.
Date: Sat, 2 Jun 2018 00:54:28 +0800	[thread overview]
Message-ID: <20180601165428.gtefyay2dlus754p@gondor.apana.org.au> (raw)
In-Reply-To: <152782824957.30340.14092720576731091742.stgit@noble>

On Fri, Jun 01, 2018 at 02:44:09PM +1000, NeilBrown wrote:
> Using rht_dereference_bucket() to dereference
> ->future_tbl looks like a type error, and could be confusing.
> Using rht_dereference_rcu() to test a pointer for NULL
> adds an unnecessary barrier - rcu_access_pointer() is preferred
> for NULL tests when no lock is held.
> 
> This uses 3 different ways to access ->future_tbl.
> - if we know the mutex is held, use rht_dereference()
> - if we don't hold the mutex, and are only testing for NULL,
>   use rcu_access_pointer()
> - otherwise (using RCU protection for true dereference),
>   use rht_dereference_rcu().
> 
> Note that this includes a simplification of the call to
> rhashtable_last_table() - we don't do an extra dereference
> before the call any more.
> 
> Signed-off-by: NeilBrown <neilb@suse.com>

Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

  reply	other threads:[~2018-06-01 16:54 UTC|newest]

Thread overview: 67+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-06-01  4:44 [RFC PATCH 00/18] Assorted rhashtable improvements NeilBrown
2018-06-01  4:44 ` [PATCH 11/18] rhashtable: further improve stability of rhashtable_walk NeilBrown
2018-06-01  4:44 ` [PATCH 17/18] rhashtable: rename rht_for_each*continue as *from NeilBrown
2018-06-01  4:44 ` [PATCH 10/18] rhashtable: remove rhashtable_walk_peek() NeilBrown
2018-06-02 15:48   ` Herbert Xu
2018-06-04  0:30     ` NeilBrown
2018-06-04  1:18       ` Tom Herbert
2018-06-04  2:09         ` NeilBrown
2018-06-04 21:31           ` Tom Herbert
2018-06-04 22:13             ` Tom Herbert
2018-06-05  1:24               ` NeilBrown
2018-06-05  1:00             ` NeilBrown
     [not found]               ` <CALx6S36Ce-rXQMzmFYZVPGD10Bo6udvRAHiZ5gWwnzVwoTVv0w@mail.gmail.com>
2018-06-06  5:07                 ` NeilBrown
2018-06-07  2:45                   ` [PATCH - RFC] rhashtable: add rhashtable_walk_last_seen() NeilBrown
2018-06-07  2:46                     ` [PATCH - RFC] rhashtable: implement rhashtable_walk_peek() using rhashtable_walk_last_seen() NeilBrown
     [not found]                       ` <CALx6S35GgUOd0dPgv7P96wNNTv5pN7fij0pcAoccqcSWZhvY7Q@mail.gmail.com>
2018-06-12  2:48                         ` [PATCH RFC v2] " NeilBrown
2018-06-14 17:41                           ` Tom Herbert
2018-06-15  4:23                             ` Herbert Xu
2018-06-15  5:31                               ` NeilBrown
2018-06-01  4:44 ` [PATCH 18/18] rhashtable: add rhashtable_walk_delay_rehash() NeilBrown
2018-06-01  4:44 ` [PATCH 14/18] rhashtable: allow rht_bucket_var to return NULL NeilBrown
2018-06-01  4:44 ` [PATCH 15/18] rhashtable: use bit_spin_locks to protect hash bucket NeilBrown
2018-06-02  5:03   ` Herbert Xu
2018-06-02  9:53     ` Eric Dumazet
2018-06-04  0:25       ` NeilBrown
2018-06-04  2:52         ` [PATCH 15a/18] rhashtables: add lockdep tracking to bucket bit-spin-locks NeilBrown
2018-06-04 18:16           ` Simon Horman
2018-06-04 21:37             ` NeilBrown
2018-06-01  4:44 ` [PATCH 01/18] rhashtable: silence RCU warning in rhashtable_test NeilBrown
2018-06-01  4:44 ` [PATCH 07/18] rhashtable: use cmpxchg() to protect ->future_tbl NeilBrown
2018-06-01 16:44   ` Herbert Xu
2018-06-01  4:44 ` [PATCH 13/18] rhashtable: don't hold lock on first table throughout insertion NeilBrown
2018-06-01  4:44 ` [PATCH 16/18] rhashtable: allow percpu element counter NeilBrown
2018-06-01  4:44 ` [PATCH 03/18] rhashtable: remove nulls_base and related code NeilBrown
2018-06-07  2:49   ` NeilBrown
2018-06-13  6:25     ` Herbert Xu
2018-06-01  4:44 ` [PATCH 08/18] rhashtable: clean up dereference of ->future_tbl NeilBrown
2018-06-01 16:54   ` Herbert Xu [this message]
2018-06-01  4:44 ` [PATCH 06/18] rhashtable: simplify nested_table_alloc() and rht_bucket_nested_insert() NeilBrown
2018-06-01 16:28   ` Herbert Xu
2018-06-01  4:44 ` [PATCH 09/18] rhashtable: use cmpxchg() in nested_table_alloc() NeilBrown
2018-06-01  4:44 ` [PATCH 05/18] rhashtable: simplify INIT_RHT_NULLS_HEAD() NeilBrown
2018-06-01 16:24   ` Herbert Xu
2018-06-01  4:44 ` [PATCH 12/18] rhashtable: add rhashtable_walk_prev() NeilBrown
2018-06-01  4:44 ` [PATCH 02/18] rhashtable: split rhashtable.h NeilBrown
2018-06-01 10:48   ` Herbert Xu
2018-06-01  4:44 ` [PATCH 04/18] rhashtable: detect when object movement might have invalidated a lookup NeilBrown
2018-06-01 16:06   ` Herbert Xu
2018-06-04  3:38     ` NeilBrown
2018-07-06  7:08     ` [PATCH resend] " NeilBrown
2018-07-12  5:46       ` David Miller
2018-07-12  5:48         ` David Miller
2018-07-15 23:55           ` NeilBrown
2018-07-15 23:57           ` [PATCH - revised] " NeilBrown
2018-07-16  0:51             ` Herbert Xu
2018-07-16  1:23               ` NeilBrown
2018-07-16  2:16                 ` Herbert Xu
2018-07-16  3:26                   ` NeilBrown
2018-07-17  6:30                     ` Herbert Xu
2018-07-20  6:24                       ` NeilBrown
2018-07-18 20:14             ` David Miller
2018-07-20  6:30               ` NeilBrown
2018-07-20  6:43                 ` David Miller
2018-07-20  7:09                   ` NeilBrown
2018-07-23  1:56               ` [PATCH net-next] rhashtable: detect when object movement between tables " NeilBrown
2018-07-26 20:55                 ` David Miller
2018-07-26 22:04                   ` NeilBrown

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