linux-kernel - Re: call_function_many: fix list delete vs add race

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Message-ID: <20110201141301.GA23646@linux.vnet.ibm.com>
Date:	Tue, 1 Feb 2011 06:13:01 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Milton Miller <miltonm@....com>, akpm@...ux-foundation.org,
	Anton Blanchard <anton@...ba.org>,
	xiaoguangrong@...fujitsu.com, mingo@...e.hu, jaxboe@...ionio.com,
	npiggin@...il.com, rusty@...tcorp.com.au,
	linux-kernel@...r.kernel.org
Subject: Re: call_function_many: fix list delete vs add race

On Tue, Feb 01, 2011 at 03:46:26PM +1000, Linus Torvalds wrote:
> On Tue, Feb 1, 2011 at 2:45 PM, Paul E. McKenney
> <paulmck@...ux.vnet.ibm.com> wrote:
> > On Tue, Feb 01, 2011 at 12:43:56PM +1000, Linus Torvalds wrote:
> >>
> >> That said, I do think that if your memory ordering is much weaker than
> >> x86, you are going to see bugs that most testers don't see, and it
> >> simply might not be worth it.
> >
> > IBM's CPUs do split the difference, with s390 having somewhat stronger
> > ordering than x86, and with powerpc being rather weaker
> 
> I'm not talking about memory ordering as done by the cpu, but as done
> by the spinlock operations. They can be arbitrarily strong, even if
> the CPU architecture itself might be weakly ordered.

Got it.

[ . . . ]

> Quite frankly, the POWER case is made worse by the fact that the
> synchronization primitives have this total confusion about "pipeline"
> synchronization due to historical implementation oddities etc. Talk
> about crazy. The whole "isync" vs "sync" vs "lwsync" thing is just an
> embarrassment.

I am always ready to exploit embarrassing parallelism!

							Thanx, Paul
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