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

[Ingo Molnar]

* Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> 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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/