From: Roman Gushchin <klamm@yandex-team•ru>
To: David Laight <David.Laight@ACULAB•COM>
Cc: Eric Dumazet <eric.dumazet@gmail•com>,
paulmck@linux•vnet.ibm.com, Dipankar Sarma <dipankar@in•ibm.com>,
zhmurov@yandex-team•ru, linux-kernel@vger•kernel.org,
netdev@vger•kernel.org, "David S. Miller" <davem@davemloft•net>,
Alexey Kuznetsov <kuznet@ms2•inr.ac.ru>,
James Morris <jmorris@namei•org>,
Hideaki YOSHIFUJI <yoshfuji@linux-ipv6•org>,
Patrick McHardy <kaber@trash•net>
Subject: Re: [PATCH v2] rcu: fix a race in hlist_nulls_for_each_entry_rcu macro
Date: Wed, 22 May 2013 17:55:21 +0400 [thread overview]
Message-ID: <519CCE49.4050308@yandex-team.ru> (raw)
In-Reply-To: <AE90C24D6B3A694183C094C60CF0A2F6026B7246@saturn3.aculab.com>
On 22.05.2013 17:27, David Laight wrote:
>> So yes, the patch appears to fix the bug, but it sounds not logical to
>> me.
>
> I was confused because the copy of the code I found was different
> (it has some checks for reusaddr - which force a function call in the
> loop).
>
> The code being compiled is:
>
> begin:
> result = NULL;
> badness = -1;
> udp_portaddr_for_each_entry_rcu(sk, node, &hslot2->head) {
> score = compute_score2(sk, net, saddr, sport,
> daddr, hnum, dif);
> if (score > badness) {
> result = sk;
> badness = score;
> if (score == SCORE2_MAX)
> goto exact_match;
> }
> }
> /*
> * if the nulls value we got at the end of this lookup is
> * not the expected one, we must restart lookup.
> * We probably met an item that was moved to another chain.
> */
> if (get_nulls_value(node) != slot2)
> goto begin;
>
> Which is entirely inlined - so the compiler is allowed to assume
> that no other code modifies any of the data.
> Hence it is allowed to cache the list head value.
> Indeed it could convert the last line to "for (;;);".
>
> A asm volatile ("":::"memory") somewhere would fix it.
>
Yes, it does. It was my first attempt to fix the issue.
But putting such instructions into each such cycle isn't a good idea, IMHO.
Regards,
Roman
next prev parent reply other threads:[~2013-05-22 13:55 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-05-21 9:05 [PATCH] rcu: fix a race in hlist_nulls_for_each_entry_rcu macro Roman Gushchin
2013-05-21 10:40 ` David Laight
2013-05-21 11:55 ` Roman Gushchin
2013-05-21 13:42 ` David Laight
2013-05-21 12:09 ` Paul E. McKenney
2013-05-21 12:46 ` Roman Gushchin
2013-05-21 12:58 ` Paul E. McKenney
2013-05-21 13:37 ` Eric Dumazet
2013-05-21 13:44 ` Eric Dumazet
2013-05-21 14:47 ` Roman Gushchin
2013-05-21 15:16 ` Eric Dumazet
2013-05-21 15:51 ` Roman Gushchin
2013-05-21 15:38 ` Eric Dumazet
2013-05-21 15:51 ` Roman Gushchin
2013-05-21 18:12 ` [PATCH v2] " Roman Gushchin
2013-05-22 2:01 ` Eric Dumazet
2013-05-22 5:49 ` Eric Dumazet
2013-05-22 11:58 ` Roman Gushchin
2013-05-22 12:30 ` Eric Dumazet
2013-05-22 13:07 ` Roman Gushchin
2013-05-22 17:45 ` Paul E. McKenney
2013-05-22 19:17 ` Roman Gushchin
2013-05-25 11:37 ` Paul E. McKenney
2013-05-27 11:34 ` Roman Gushchin
2013-05-27 17:55 ` Roman Gushchin
2013-05-28 0:12 ` Eric Dumazet
2013-05-28 9:10 ` Roman Gushchin
2013-05-29 0:34 ` Eric Dumazet
2013-05-29 1:31 ` Paul E. McKenney
2013-05-29 5:08 ` Eric Dumazet
2013-05-29 10:09 ` Roman Gushchin
2013-05-29 19:06 ` Eric Dumazet
2013-05-30 8:25 ` Roman Gushchin
2013-06-02 23:31 ` Eric Dumazet
2013-06-03 2:58 ` David Miller
2013-06-03 3:12 ` Eric Dumazet
2013-06-03 3:27 ` David Miller
2013-06-03 3:42 ` Paul E. McKenney
2013-06-03 3:47 ` Eric Dumazet
2013-06-03 3:49 ` David Miller
2013-06-03 6:05 ` Paul E. McKenney
2013-06-10 18:29 ` Boris B. Zhmurov
2013-06-10 18:51 ` Eric Dumazet
2013-06-03 3:48 ` Paul E. McKenney
2013-06-03 3:42 ` Paul E. McKenney
2013-05-29 9:17 ` Roman Gushchin
2013-05-29 1:19 ` Paul E. McKenney
2013-05-22 13:27 ` David Laight
2013-05-22 13:36 ` Eric Dumazet
2013-05-22 14:23 ` David Laight
2013-05-22 13:55 ` Roman Gushchin [this message]
2013-05-22 9:58 ` Paul E. McKenney
2013-05-22 12:28 ` Eric Dumazet
2013-05-22 13:00 ` Paul E. McKenney
2013-05-22 14:16 ` Eric Dumazet
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