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From: Peter Zijlstra <peterz@infradead.org>
To: Florian Westphal <fw@strlen.de>
Cc: Anatol Pomozov <anatol.pomozov@gmail.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	paulmck@linux.ibm.com, LKML <linux-kernel@vger.kernel.org>
Subject: Re: seqcount usage in xt_replace_table()
Date: Fri, 11 Jan 2019 09:34:11 +0100	[thread overview]
Message-ID: <20190111083411.GM1900@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190110222920.jqpzzv74huc2lb7f@breakpoint.cc>

On Thu, Jan 10, 2019 at 11:29:20PM +0100, Florian Westphal wrote:
> Peter Zijlstra <peterz@infradead.org> wrote:
> > Would using synchronize_rcu() not also mean you can get rid of that
> > xt_write_recseq*() stuff entirely?
> 
> No, because those are used to synchronize with cpus that read
> the ruleset counters, see
> 
> net/ipv4/netfilter/ip_tables.c:get_counters().

Ah, bummer :/

> > Anyway, synchronize_rcu() can also take a little while, but I don't
> > think anywere near 30 seconds.
> 
> Ok, I think in that case it would be best to just replace the
> recseq value sampling with smp_mb + synchronize_rcu plus a comment
> that explains why its done.

synchronize_rcu() implies smp_mb() on all CPUs.

  reply	other threads:[~2019-01-11  8:34 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-08 19:33 seqcount usage in xt_replace_table() Anatol Pomozov
2019-01-08 22:37 ` Florian Westphal
2019-01-10 12:41   ` Peter Zijlstra
2019-01-10 12:53     ` Dmitry Vyukov
2019-01-10 20:18       ` Peter Zijlstra
2019-01-10 14:48     ` Florian Westphal
2019-01-10 20:20       ` Peter Zijlstra
2019-01-10 20:25       ` Peter Zijlstra
2019-01-10 22:29         ` Florian Westphal
2019-01-11  8:34           ` Peter Zijlstra [this message]
2019-01-11 14:08             ` Paul E. McKenney
2019-01-10 14:52     ` Paul E. McKenney
2019-01-09  0:02 ` Andrea Parri
2019-01-09  0:36   ` Anatol Pomozov
2019-01-09  5:35     ` Dmitry Vyukov
2019-01-09 11:24     ` Andrea Parri
2019-01-09 11:55       ` Dmitry Vyukov
2019-01-09 12:11         ` Andrea Parri
2019-01-09 12:29           ` Dmitry Vyukov
2019-01-09 17:10             ` Paul E. McKenney
2019-01-10  8:49               ` Dmitry Vyukov
2019-01-10 12:30                 ` Andrea Parri
2019-01-10 12:38                   ` Dmitry Vyukov
2019-01-10 12:46                     ` Andrea Parri
2019-01-10 13:25                       ` Dmitry Vyukov
2019-01-10 14:50                     ` Paul E. McKenney
2019-01-10 12:44 ` Peter Zijlstra
2019-01-10 12:54   ` Dmitry Vyukov

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