Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757069AbZCBW5S (ORCPT ); Mon, 2 Mar 2009 17:57:18 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754756AbZCBW5E (ORCPT ); Mon, 2 Mar 2009 17:57:04 -0500 Received: from mx2.redhat.com ([66.187.237.31]:43248 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750910AbZCBW5C (ORCPT ); Mon, 2 Mar 2009 17:57:02 -0500 Message-ID: <49AC63FA.70801@redhat.com> Date: Mon, 02 Mar 2009 17:55:54 -0500 From: Masami Hiramatsu User-Agent: Thunderbird 2.0.0.19 (X11/20090105) MIME-Version: 1.0 To: Ingo Molnar CC: Mathieu Desnoyers , Andrew Morton , Nick Piggin , Steven Rostedt , Andi Kleen , linux-kernel@vger.kernel.org, Thomas Gleixner , Peter Zijlstra , Frederic Weisbecker , Linus Torvalds , Arjan van de Ven , Rusty Russell , "H. Peter Anvin" , Steven Rostedt Subject: Re: [RFC][PATCH] x86: make text_poke() atomic References: <20090223173108.GB1441@Krystal> <49A82851.5080707@redhat.com> <20090227180724.GA17947@Krystal> <49A83237.40604@redhat.com> <20090227185316.GA19811@Krystal> <49A853CD.3020607@redhat.com> <49AC10E9.1090102@redhat.com> <20090302171914.GB21735@Krystal> <49AC5A87.7000604@redhat.com> <20090302222254.GA31962@elte.hu> In-Reply-To: <20090302222254.GA31962@elte.hu> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3385 Lines: 107 Ingo Molnar wrote: > * Masami Hiramatsu 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 -- 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/