From: Andrew Morton <akpm@osdl.org>
To: paulmck@us.ibm.com
Cc: oleg@tv-sign.ru, vatsa@in.ibm.com, linux-kernel@vger.kernel.org,
dipankar@in.ibm.com
Subject: Re: [PATCH] Fix RCU race in access of nohz_cpu_mask
Date: Sun, 11 Dec 2005 20:32:26 -0800 [thread overview]
Message-ID: <20051211203226.4deafd59.akpm@osdl.org> (raw)
In-Reply-To: <20051212031053.GA8748@us.ibm.com>
"Paul E. McKenney" <paulmck@us.ibm.com> wrote:
>
> 1. wmb() guarantees that any writes preceding the wmb() will
> be seen by the interconnect before any writes following the
> wmb(). But this applies -only- to the writes executed by
> the CPU doing the wmb().
>
> 2. rmb() guarantees that any changes seen by the interconnect
> preceding the rmb() will be seen by any reads following the
> rmb(). Again, this applies only to reads executed by the
> CPU doing the wmb(). However, the changes might be due to
> any CPU.
>
> 3. mb() combines the guarantees made by rmb() and wmb().
So foo_mb() in preemptible code is potentially buggy.
I guess we assume that a context switch accidentally did enough of the
right types of barriers for things to work OK.
next prev parent reply other threads:[~2005-12-12 4:32 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-12-08 19:31 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
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 [this message]
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
-- strict thread matches above, loose matches on Subject: below --
2005-12-05 11:02 Srivatsa Vaddagiri
2005-12-08 0:37 ` Andrew Morton
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