Re: [PATCH] modules fix incorrect percpu usage

[Steven Rostedt]

On Tue, 2010-03-30 at 16:24 -0400, Mathieu Desnoyers wrote:

> > Why do you beleive this should be backported to -stable?  What are the
> > user-visible effects of this change?
> > 
> 
> As for the user-visible impact of this specific patch, I guess nobody noticed
> any problem because we've been lucky enough that the compiler did not generate
> the inappropriate optimization pattern there.
> 
> This inappropriate use of per_cpu_ptr() elsewhere (in __module_ref_addr() from
> module.h) caused a NULL pointer exception on Randy's machine.
> 
> So either we consider that the code is better left untouched, or we apply this
> patch to module.c in order to prevent compiler optimizations from subtly
> breaking the generated assembly with specific configurations of the current or
> future versions of the compiler. At that level, it becomes a policy question
> about what should go in -stable, for which I will defer to Greg and you. I would
> perfectly understand if you consider that it does not belong to -stable, because
> there is no perceived user impact so far.

I don't know. A possible "NULL pointer dereference" seems to me to be a
pretty big user visible impact.

I guess the question is, what's the risk of adding this change?

-- Steve


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