Messages in this thread |  | | | Date | Tue, 3 Mar 2009 00:09:15 +0100 | | From | Ingo Molnar <> | | Subject | Re: [RFC][PATCH] x86: make text_poke() atomic |
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* Masami Hiramatsu <mhiramat@redhat.com> wrote:
> > > Ingo Molnar wrote: > > * 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. > > Thank you for review, > > > > > (Note, i could not try your patch because it has widespread > > whitespace damage - please watch out for this for future > > patches.) > > Oops, it was my mis-setting... > > > > >> +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. > > Sure. > > > > > 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. > > Oh, it's a good idea! fixmaps must make it simpler. > > > > > In exchange it will be conceptually simpler, and will also scale > > much better than a global spinlock. What do you think? > > I think even if I use fixmaps, we have to use a spinlock to protect > the fixmap area from other threads...
that's why i suggested to use an atomic-kmap, not a fixmap.
Ingo
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