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SubjectRe: [PATCH 1/1] x86: fix text_poke

* Linus Torvalds <torvalds@linux-foundation.org> wrote:

> No. That whole code sequence is total and utter crap. It needs to be
> rewritten.
>
> It first does a BUG_ON() if it's not naturally aligned (because that
> wouldn't be atomic), and then it has code for page crossing! What a
> TOTAL PIECE OF SH*T!
>
> Hint:
> - if it's naturally aligned, it couldn't be page crossing ANYWAY
> - and if it was a page-crosser, it sure as hell couldn't be atomic!
>
> The code is just crap, crap, crap. It needs to be rewritten from
> scratch. I'll have a patch soonish.

yeah :(

it seems that this code only worked because text_poke_early() [which can
take arbitrary length and alignment] does most of the patching, it is
the real code-patching machinery that is used during early bootup - and
that's not used later on.

text_poke() itself only applies/unapplies the LOCK prefix - a single
byte. We shouldnt be doing that at all: the cost of LOCK is
insignificant (a few cycles) and most systems are SMP anyway.

any other type of code patching should use stop_machine_run(), where
every CPU is stopped with irqs disabled.

Ingo


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