Messages in this thread |  | | | Date | Thu, 21 Aug 2008 04:47:45 -0700 | | From | "Paul E. McKenney" <> | | Subject | Re: [ANNOUNCE] mdb: Merkey's Linux Kernel Debugger 2.6.27-rc4 released | |
On Thu, Aug 21, 2008 at 01:02:48PM +0200, Peter Zijlstra wrote:
> 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@wolfmountaingroup.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.
Let's face it, the C standard does not support concurrency, so we are
all in a state of sin in any case, forced to rely on combinations of
gcc-specific non-standard language extensions and assembly language.
Could be worse!!!
Thanx, Paul
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