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Message-Id: <200708241407.26180.ak@suse.de>
Date: Fri, 24 Aug 2007 14:07:25 +0200
From: Andi Kleen <ak@...e.de>
To: Denys Vlasenko <vda.linux@...glemail.com>
Cc: Satyam Sharma <satyam@...radead.org>,
Heiko Carstens <heiko.carstens@...ibm.com>,
Herbert Xu <herbert@...dor.apana.org.au>,
Chris Snook <csnook@...hat.com>, clameter@....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>,
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] i386: Fix a couple busy loops in mach_wakecpu.h:wait_for_init_deassert()
On Friday 24 August 2007 13:59:32 Denys Vlasenko wrote:
> On Thursday 16 August 2007 01:39, Satyam Sharma wrote:
> >
> > static inline void wait_for_init_deassert(atomic_t *deassert)
> > {
> > - while (!atomic_read(deassert));
> > + while (!atomic_read(deassert))
> > + cpu_relax();
> > return;
> > }
>
> For less-than-briliant people like me, it's totally non-obvious that
> cpu_relax() is needed for correctness here, not just to make P4 happy.
I find it also non obvious. It would be really better to have a barrier
or equivalent (volatile or variable clobber) in the atomic_read()
> IOW: "atomic_read" name quite unambiguously means "I will read
> this variable from main memory". Which is not true and creates
> potential for confusion and bugs.
Agreed.
-Andi
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