Re: [Xen-devel] [PATCH v2 2/5] tools: add routine to get CMT L3 event mask

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Andrew Cooper writes ("Re: [Xen-devel] [PATCH v2 2/5] tools: add routine to get 
CMT L3 event mask"):
> Other culprits are xc_get_max_nodes(), xc_get_max_cpus(), 4 instances in
> xc_psr.c and most things in xc_offline_page.c which appears to have
> static structures for domain context.  The "pluggable loader"
> infrastructure in xc_dom.c also appears to be thread-unsafe.
>
> xc_dom_decompress_unsafe.c also uses static data, but "unsafe" in the
> name might be a sufficient guard?

I will look at these tomorrow.

> No aggressively optimising compiler is going to perform partial writes
> on a naturally aligned integer, so I stand by my comment when applied to
> the common case.

You misunderstand.  An aggressively optimising compiler might be able
to "prove" (perhaps through whole program analysis - we have link-time
optimisation nowadays) various falsehoods about the way these
variables are used.

The resulting generated machine code might be arbitrarily bad, up to
and including missing important parts of the whole program.

I'm not aware of any compilers which currently take "advantge" of
thread safety "bugs" (really, just spec-violations) but I think this
is just a matter of time.

Ian.

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