Messages in this thread |  | | Date | Mon, 02 Mar 2009 17:55:54 -0500 | | From | Masami Hiramatsu <> | | Subject | Re: [RFC][PATCH] x86: make text_poke() atomic |
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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...
> > Ingo > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/
-- Masami Hiramatsu
Software Engineer Hitachi Computer Products (America) Inc. Software Solutions Division
e-mail: mhiramat@redhat.com
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