Messages in this thread |  | | Date | Mon, 2 Mar 2009 23:22:54 +0100 | | From | Ingo Molnar <> | | Subject | Re: [RFC][PATCH] x86: make text_poke() atomic |
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* Masami Hiramatsu <mhiramat@redhat.com> wrote:
> Mathieu Desnoyers wrote: >> * Masami Hiramatsu (mhiramat@redhat.com) wrote: >>> Index: linux-2.6/init/main.c >>> =================================================================== >>> --- linux-2.6.orig/init/main.c >>> +++ linux-2.6/init/main.c >>> @@ -676,6 +676,9 @@ asmlinkage void __init start_kernel(void >>> taskstats_init_early(); >>> delayacct_init(); >>> >>> +#ifdef CONFIG_X86 >>> + text_poke_init(); >>> +#endif >> >> All good, except this above. There should be an empty text_poke_init() >> in some header file, and an implementation for the X86 arch rather than >> a ifdef in init/main.c. > > Hmm, I'd rather use __weak function instead of defining it in some header > files, because text_poke() and alternatives exist only on x86. > > I know that we need to discuss cross modifying code on x86 with > Arjan or other Intel engineers. This patch may still be useful > for removing unnecessary vm_area allocation in text_poke(). > > Thank you, > > --- > > Use map_vm_area() instead of vmap() in text_poke() for > avoiding page allocation and delayed unmapping, and call > vunmap_page_range() and local_flush_tlb() directly because > this mapping is temporary and local. > > At the result of above change, text_poke() becomes atomic and > can be called from stop_machine() etc.
That looks like a good fix in itself - see a few minor details below.
(Note, i could not try your patch because it has widespread whitespace damage - please watch out for this for future patches.)
> +static struct vm_struct *text_poke_area[2]; > +static DEFINE_SPINLOCK(text_poke_lock); > + > +void __init text_poke_init(void) > +{ > + text_poke_area[0] = get_vm_area(PAGE_SIZE, VM_ALLOC); > + text_poke_area[1] = get_vm_area(2 * PAGE_SIZE, VM_ALLOC); > + BUG_ON(!text_poke_area[0] || !text_poke_area[1]);
BUG_ON() for non-100%-essential init code is a no-no. Please change it to WARN_ON() so that people have a chance to report i.
Also, i think all these vma complications came from the decision to use vmap - and vmap enhancements in .29 complicated this supposedly-simple interface.
So perhaps another approach to (re-)consider would be to go back to atomic fixmaps here. It spends 3 slots but that's no big deal.
In exchange it will be conceptually simpler, and will also scale much better than a global spinlock. What do you think?
Ingo
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