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Date: Fri, 17 Aug 2007 15:41:28 +1000 From: Paul Mackerras <paulus@...ba.org> To: Herbert Xu <herbert@...dor.apana.org.au> Cc: Stefan Richter <stefanr@...6.in-berlin.de>, Satyam Sharma <satyam@...radead.org>, Christoph Lameter <clameter@....com>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, Chris Snook <csnook@...hat.com>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, linux-arch@...r.kernel.org, Linus Torvalds <torvalds@...ux-foundation.org>, netdev@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>, ak@...e.de, heiko.carstens@...ibm.com, davem@...emloft.net, schwidefsky@...ibm.com, wensong@...ux-vs.org, horms@...ge.net.au, wjiang@...ilience.com, cfriesen@...tel.com, zlynx@....org, rpjday@...dspring.com, jesper.juhl@...il.com, segher@...nel.crashing.org Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures Herbert Xu writes: > On Fri, Aug 17, 2007 at 03:09:57PM +1000, Paul Mackerras wrote: > > Herbert Xu writes: > > > > > Can you find an actual atomic_read code snippet there that is > > > broken without the volatile modifier? > > > > There are some in arch-specific code, for example line 1073 of > > arch/mips/kernel/smtc.c. On mips, cpu_relax() is just barrier(), so > > the empty loop body is ok provided that atomic_read actually does the > > load each time around the loop. > > A barrier() is all you need to force the compiler to reread > the value. > > The people advocating volatile in this thread are talking > about code that doesn't use barrier()/cpu_relax(). Did you look at it? Here it is: /* Someone else is initializing in parallel - let 'em finish */ while (atomic_read(&idle_hook_initialized) < 1000) ; Paul. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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