linux-kernel - Re: [ANNOUNCE] mdb: Merkey's Linux Kernel Debugger 2.6.27-rc4 released

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Date:	Thu, 21 Aug 2008 13:02:48 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stefan Richter <stefanr@...6.in-berlin.de>
Cc:	jmerkey@...fmountaingroup.com, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Paul E McKenney <paulmck@...ux.vnet.ibm.com>,
	David Howells <dhowells@...hat.com>
Subject: Re: [ANNOUNCE] mdb: Merkey's Linux Kernel Debugger
	2.6.27-rc4	released

On Thu, 2008-08-21 at 12:57 +0200, Stefan Richter wrote:
> Peter Zijlstra wrote:
> > On Wed, 2008-08-20 at 20:50 -0600, jmerkey@...fmountaingroup.com wrote:
> > 
> >>  volatiles left in the code due to the previously stated
> >>  (and still present) severe breakage of the GNU compiler with SMP 
> >>  shared data.  most of the barrier() functions are just plain broken
> >>  and do not result in proper compiler behavior in this tree. 
> > 
> > Can you provide explicit detail?
> > 
> > By using barrier() the compiler should clobber all its memory and
> > registers therefore forcing a write/reload of the variable.
> 
> I hope Jeff didn't try mere barrier()s only.  smp_wmb() and smp_rmb()
> are the more relevant barrier variants for mdb, from what I remember
> when I last looked at it.

Sure, but volatile isn't a replacement for memory barriers.

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