Re: [RFC patch 08/18] cnt32_to_63 should use smp_rmb()

Mathieu Desnoyers
2008-11-07T18:00:54Z

* Andrew Morton (akpm@linux-foundation.org) wrote:
> On Fri, 07 Nov 2008 17:10:00 +0000 David Howells <dhowells@redhat.com> wrote:
>
> >
> > Andrew Morton <akpm@linux-foundation.org> wrote:
> >
> > > I'd expect it to behave in the same way as it would if the function was
> > > implemented out-of-line.
> > >
> > > But it occurs to me that the modrobe-doesnt-work thing would happen if
> > > the function _is_ inlined anyway, so we won't be doing that.
> > >
> > > Whatever. Killing this many puppies because gcc may do something so
> > > bizarrely wrong isn't justifiable.
> >
> > With gcc, you get one instance of the static variable from inside a static
> > (inline or outofline) function per .o file that invokes it, and these do not
> > merge even though they're common symbols. I asked around and the opinion
> > seems to be that this is correct C. I suppose it's the equivalent of cutting
> > and pasting a function between several files - why should the compiler assume
> > it's the same function in each?
> >
>
> OK, thanks, I guess that makes sense. For static inline. I wonder if
> `extern inline' or plain old `inline' should change it.
>
> It's one of those things I hope I never need to know about, but perhaps
> we do somewhere have static storage in an inline. Wouldn't surprise
> me, and I bet that if we do, it's a bug.

Tracepoints actually use that. It could be changed so they use :

DECLARE_TRACE() (in include/trace/group.h)
DEFINE_TRACE() (in the appropriate kernel c file)
trace_somename(); (in the code)

instead. That would actually make more sense and remove the need for
multiple declarations when the same tracepoint name is used in many
spots (this is a problem kmemtrace has, it generates a lot of tracepoint
declarations).

Mathieu

--
Mathieu Desnoyers
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