Re: [block IO crash] Re: 2.6.39-rc5-git2 boot crashs

[Linus Torvalds]

On Wed, May 4, 2011 at 2:06 PM, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> The problem is that cmpxchg *IS*NOT*AN*CMPXCHG*AT*ALL*. Not even on UP.

Btw, the really sad thing is that as far as I can tell, the
cmpxchg64_local() function that we define actually gets this *right*,
with a helper function that actually works (and disables interrupts)
and all the alternative_io() stuff to then use the right instruction
automatically if the CPU supports it, rather than making it a
hardcoded decision.

But we don't use it, because the "percpu_cmpxchg8b_double()" code
rolls its own inferior version, and has slightly different semantics
(ie the whole "return value success" thing).

So close, but yet so far.

                       Linus
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