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Open Source and information security mailing list archives
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Date: Tue, 11 Sep 2007 04:27:22 +0200 From: Segher Boessenkool <segher@...nel.crashing.org> To: Christoph Lameter <clameter@....com> Cc: Paul Mackerras <paulus@...ba.org>, heiko.carstens@...ibm.com, horms@...ge.net.au, Stefan Richter <stefanr@...6.in-berlin.de>, Satyam Sharma <satyam@...radead.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, David Miller <davem@...emloft.net>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>, ak@...e.de, cfriesen@...tel.com, rpjday@...dspring.com, Netdev <netdev@...r.kernel.org>, jesper.juhl@...il.com, linux-arch@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>, zlynx@....org, schwidefsky@...ibm.com, Chris Snook <csnook@...hat.com>, Herbert Xu <herbert@...dor.apana.org.au>, Linus Torvalds <torvalds@...ux-foundation.org>, wensong@...ux-vs.org, wjiang@...ilience.com Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures >> "volatile" has nothing to do with reordering. atomic_dec() writes >> to memory, so it _does_ have "volatile semantics", implicitly, as >> long as the compiler cannot optimise the atomic variable away >> completely -- any store counts as a side effect. > > Stores can be reordered. Only x86 has (mostly) implicit write ordering. > So no atomic_dec has no volatile semantics Read again: I said the C "volatile" construct has nothing to do with CPU memory access reordering. > and may be reordered on a variety > of processors. Writes to memory may not follow code order on several > processors. The _compiler_ isn't allowed to reorder things here. Yes, of course you do need stronger barriers for many purposes, volatile isn't all that useful you know. Segher - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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