[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <46C581AA.7020807@s5r6.in-berlin.de>
Date: Fri, 17 Aug 2007 13:08:26 +0200
From: Stefan Richter <stefanr@...6.in-berlin.de>
To: Nick Piggin <nickpiggin@...oo.com.au>
CC: Satyam Sharma <satyam@...radead.org>,
Herbert Xu <herbert@...dor.apana.org.au>,
Paul Mackerras <paulus@...ba.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Christoph Lameter <clameter@....com>,
Chris Snook <csnook@...hat.com>,
Ilpo Jarvinen <ilpo.jarvinen@...sinki.fi>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
linux-arch@...r.kernel.org, Netdev <netdev@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>, ak@...e.de,
heiko.carstens@...ibm.com, David Miller <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
Nick Piggin wrote:
> Satyam Sharma wrote:
>> And we have driver / subsystem maintainers such as Stefan
>> coming up and admitting that often a lot of code that's written to use
>> atomic_read() does assume the read will not be elided by the compiler.
>
> So these are broken on i386 and x86-64?
The ieee1394 and firewire subsystems have open, undiagnosed bugs, also
on i386 and x86-64. But whether there is any bug because of wrong
assumptions about atomic_read among them, I don't know. I don't know
which assumptions the authors made, I only know that I wasn't aware of
all the properties of atomic_read until now.
> Are they definitely safe on SMP and weakly ordered machines with
> just a simple compiler barrier there? Because I would not be
> surprised if there are a lot of developers who don't really know
> what to assume when it comes to memory ordering issues.
>
> This is not a dig at driver writers: we still have memory ordering
> problems in the VM too (and probably most of the subtle bugs in
> lockless VM code are memory ordering ones). Let's not make up a
> false sense of security and hope that sprinkling volatile around
> will allow people to write bug-free lockless code. If a writer
> can't be bothered reading API documentation
...or, if there is none, the implementation specification (as in case of
the atomic ops), or, if there is none, the implementation (as in case of
a some infrastructure code here and there)...
> and learning the Linux memory model, they can still be productive
> writing safely locked code.
Provided they are aware that they might not have the full picture of the
lockless primitives. :-)
--
Stefan Richter
-=====-=-=== =--- =---=
http://arcgraph.de/sr/
-
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/
Powered by blists - more mailing lists