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Date: Sat, 18 Aug 2007 16:35:53 +0200 From: Stefan Richter <stefanr@...6.in-berlin.de> To: Jonathan Corbet <corbet@....net>, Greg Kroah-Hartman <gregkh@...e.de> CC: Nick Piggin <nickpiggin@...oo.com.au>, paulmck@...ux.vnet.ibm.com, Herbert Xu <herbert@...dor.apana.org.au>, Paul Mackerras <paulus@...ba.org>, Satyam Sharma <satyam@...radead.org>, Christoph Lameter <clameter@....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: LDD3 pitfalls (was Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures) Nick Piggin wrote: > Stefan Richter wrote: >> Nick Piggin wrote: >> >>> I don't know why people would assume volatile of atomics. AFAIK, most >>> of the documentation is pretty clear that all the atomic stuff can be >>> reordered etc. except for those that modify and return a value. >> >> >> Which documentation is there? > > Documentation/atomic_ops.txt > > >> For driver authors, there is LDD3. It doesn't specifically cover >> effects of optimization on accesses to atomic_t. >> >> For architecture port authors, there is Documentation/atomic_ops.txt. >> Driver authors also can learn something from that document, as it >> indirectly documents the atomic_t and bitops APIs. >> > > "Semantics and Behavior of Atomic and Bitmask Operations" is > pretty direct :) > > Sure, it says that it's for arch maintainers, but there is no > reason why users can't make use of it. Note, LDD3 page 238 says: "It is worth noting that most of the other kernel primitives dealing with synchronization, such as spinlock and atomic_t operations, also function as memory barriers." I don't know about Linux 2.6.10 against which LDD3 was written, but currently only _some_ atomic_t operations function as memory barriers. Besides, judging from some posts in this thread, saying that atomic_t operations dealt with synchronization may not be entirely precise. -- Stefan Richter -=====-=-=== =--- =--=- http://arcgraph.de/sr/ - 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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