From: Andrea Arcangeli <andrea@suse.de>
To: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>,
benh@kernel.crashing.org, hugh@veritas.com, paulus@samba.org,
anton@samba.org, torvalds@osdl.org, akpm@osdl.org,
linux-kernel@vger.kernel.org
Subject: Re: Possible memory ordering bug in page reclaim?
Date: Sat, 15 Oct 2005 22:07:01 +0200 [thread overview]
Message-ID: <20051015200701.GP18159@opteron.random> (raw)
In-Reply-To: <20051015194855.GA1164@gondor.apana.org.au>
On Sun, Oct 16, 2005 at 05:48:55AM +1000, Herbert Xu wrote:
> On Sat, Oct 15, 2005 at 06:00:18PM +0000, Andrea Arcangeli wrote:
> >
> > Note that the barrier in atomic_add_negative is useless here because it
> > happens way too late, _after_ the count is decremented (not _before_)
> > so the decreased count could be already visible to the other cpu.
>
> Could you please point me to an architecture that does this?
sure see alpha:
__asm__ __volatile__(
"1: ldq_l %0,%1\n"
" addq %0,%3,%2\n"
" addq %0,%3,%0\n"
" stq_c %0,%1\n"
" beq %0,2f\n"
" mb\n"
the memory barrier is applied way after the write is visible to other
cpus, you can even get an irq before the mb and block there for some
usec.
>From a common code point of view, the barrier you mentioned in
atomic_add_negative is absolutely useless for this specific case
(setpagedirty+put_page)
next prev parent reply other threads:[~2005-10-15 20:07 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-10-15 3:28 Possible memory ordering bug in page reclaim? Nick Piggin
2005-10-15 6:17 ` Hugh Dickins
2005-10-15 7:43 ` Benjamin Herrenschmidt
2005-10-15 8:00 ` Herbert Xu
2005-10-15 16:57 ` Linus Torvalds
2005-10-15 19:29 ` David S. Miller
2005-10-15 22:17 ` Benjamin Herrenschmidt
2005-10-16 0:04 ` Nick Piggin
2005-10-15 8:59 ` Nick Piggin
2005-10-15 12:08 ` Herbert Xu
2005-10-15 13:35 ` Nick Piggin
2005-10-15 18:00 ` Andrea Arcangeli
2005-10-15 19:48 ` Herbert Xu
2005-10-15 20:07 ` Andrea Arcangeli [this message]
2005-10-15 23:07 ` David S. Miller
2005-10-16 19:36 ` Ivan Kokshaysky
2005-10-17 4:29 ` David S. Miller
2005-10-17 7:23 ` Ivan Kokshaysky
2005-10-17 11:28 ` Andrea Arcangeli
2005-10-15 22:16 ` Benjamin Herrenschmidt
2005-10-15 23:13 ` David S. Miller
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