Date: Sun, 16 Oct 2005 05:48:55 +1000
To: Andrea Arcangeli <andrea@suse.de>
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?
Message-ID: <20051015194855.GA1164@gondor.apana.org.au>
References: <4350C4F6.4030807@yahoo.com.au> <E1EQkpc-0007FI-00@gondolin.me.apana.org.au> <20051015180018.GN18159@opteron.random>
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From: Herbert Xu <herbert@gondor.apana.org.au>
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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?

This assumption is in fact made in a number of places in the kernel
where constructs such as atomic_add_negative or atomic_dec_and_test
are used and assumed to imply a memory barrier.

Thanks,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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