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From: Oleg Nesterov <oleg@tv-sign.ru>
To: vatsa@in.ibm.com
Cc: Keith Owens <kaos@ocs.com.au>,
	Rusty Russell <rusty@rustcorp.com.au>,
	ajwade@cpe001346162bf9-cm0011ae8cd564.cpe.net.cable.rogers.com,
	linux-kernel@vger.kernel.org,
	Dipankar Sarma <dipankar@in.ibm.com>,
	"Paul E. McKenney" <paulmck@us.ibm.com>,
	Andrew Morton <akpm@osdl.org>, Ingo Molnar <mingo@elte.hu>
Subject: Re: Semantics of smp_mb() [was : Re: [PATCH] Fix RCU race in access of  nohz_cpu_mask ]
Date: Mon, 12 Dec 2005 22:33:22 +0300	[thread overview]
Message-ID: <439DD082.9508C87C@tv-sign.ru> (raw)
In-Reply-To: <20051212084112.GA3934@in.ibm.com>

Srivatsa Vaddagiri wrote:
> 
> Oleg, with all these inputs, I consider the patch I had sent to be correct.

Yes, I think so. My suspects were due to my misunderstanding.
I was wrong when I said that we can ignore rmb() part of mb()
in case when start_hz_timer() runs after rcu_start_batch().

	rcp->cur++;
	// ->cur will be visible to other cpus
	// _before_ we will *READ* nohz_cpu_mask.
	// we don't have any 'timing' problems.
	// In other words: if another cpu does not
	// see the new value - we did not read this
	// mask yet.
	smp_mb();

Thanks for your patience.

> P.S :- Thanks to everybody who reponded clarifying this subject.

Yes! it was really helpful, thanks to all. I think it would be great
to have Paul's very clear (and short!) explanation somewhere in
Documentation/.

Oleg.

  reply	other threads:[~2005-12-12 18:18 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2005-12-08 19:31 [PATCH] Fix RCU race in access of nohz_cpu_mask Oleg Nesterov
2005-12-09  2:46 ` Srivatsa Vaddagiri
2005-12-09 19:17   ` Oleg Nesterov
2005-12-10 15:19     ` Srivatsa Vaddagiri
2005-12-10 18:55       ` Oleg Nesterov
2005-12-11 17:41         ` Semantics of smp_mb() [was : Re: [PATCH] Fix RCU race in access of nohz_cpu_mask ] Srivatsa Vaddagiri
2005-12-11 21:21           ` Andrew James Wade
2005-12-11 23:45             ` Rusty Russell
2005-12-12  0:49               ` Keith Owens
2005-12-12  8:41                 ` Srivatsa Vaddagiri
2005-12-12 19:33                   ` Oleg Nesterov [this message]
2005-12-13  5:20                     ` Paul E. McKenney
2005-12-13  5:07               ` Andrew James Wade
2005-12-13  5:43                 ` Paul E. McKenney
2005-12-13 11:20                 ` Andi Kleen
2005-12-13 16:20                   ` Paul E. McKenney
2005-12-13 22:27                     ` Keith Owens
2005-12-13 22:50                       ` Paul E. McKenney
2005-12-14  1:12                         ` Andi Kleen
2005-12-14  1:46                           ` Paul E. McKenney
2005-12-15 21:15                       ` Semantics of smp_mb() Roland Dreier
2005-12-16  7:46                       ` Semantics of smp_mb() [was : Re: [PATCH] Fix RCU race in access of nohz_cpu_mask ] Jeremy Higdon
2006-03-13 18:39                         ` Paul E. McKenney
2006-03-31  4:56                           ` Jeremy Higdon
2006-03-31  6:18                             ` Paul E. McKenney
2006-03-31 23:38                             ` Jesse Barnes
2005-12-12  3:10         ` [PATCH] Fix RCU race in access of nohz_cpu_mask Paul E. McKenney
2005-12-12  4:32           ` Andrew Morton
2005-12-12  4:38             ` David S. Miller
2005-12-12  4:47               ` Nick Piggin
2005-12-12  4:49             ` Paul Mackerras
2005-12-12  6:27             ` Keith Owens
2005-12-09  2:56 ` Srivatsa Vaddagiri

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