Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756761AbZCFTJT (ORCPT ); Fri, 6 Mar 2009 14:09:19 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752886AbZCFTJF (ORCPT ); Fri, 6 Mar 2009 14:09:05 -0500 Received: from mx2.mail.elte.hu ([157.181.151.9]:34953 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752499AbZCFTJE (ORCPT ); Fri, 6 Mar 2009 14:09:04 -0500 Date: Fri, 6 Mar 2009 20:08:28 +0100 From: Ingo Molnar To: Masami Hiramatsu Cc: Mathieu Desnoyers , Andrew Morton , Nick Piggin , Steven Rostedt , Andi Kleen , Linux Kernel Mailing List , Thomas Gleixner , Peter Zijlstra , Frederic Weisbecker , Linus Torvalds , Arjan van de Ven , Rusty Russell , "H. Peter Anvin" Subject: Re: [PATCH -tip 4/4] Atomic text_poke() with fixmap take2 Message-ID: <20090306190828.GA28582@elte.hu> References: <49B1428A.9050500@redhat.com> <49B14352.2040705@redhat.com> <20090306181356.GD14236@Krystal> <49B16C69.6060203@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <49B16C69.6060203@redhat.com> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2124 Lines: 54 * Masami Hiramatsu wrote: > @@ -523,14 +526,17 @@ void *__kprobes text_poke(void *addr, co > pages[1] = virt_to_page(addr + PAGE_SIZE); > } > BUG_ON(!pages[0]); > - if (!pages[1]) > - nr_pages = 1; > - vaddr = vmap(pages, nr_pages, VM_MAP, PAGE_KERNEL); > - BUG_ON(!vaddr); > - local_irq_disable(); > + local_irq_save(flags); > + set_fixmap(FIX_TEXT_POKE0, page_to_phys(pages[0])); > + if (pages[1]) > + set_fixmap(FIX_TEXT_POKE1, page_to_phys(pages[1])); > + vaddr = (char *)fix_to_virt(FIX_TEXT_POKE0); > memcpy(&vaddr[(unsigned long)addr & ~PAGE_MASK], opcode, len); > - local_irq_enable(); > - vunmap(vaddr); > + clear_fixmap(FIX_TEXT_POKE0); > + if (pages[1]) > + clear_fixmap(FIX_TEXT_POKE1); > + local_flush_tlb(); > + local_irq_restore(flags); > sync_core(); I'm not sure at all about this widening of the irq-atomic section and the idea of allowing non-locked access on single-CPU situations - we dont really want to micro-optimize any of this on such a level, holding the text lock is a robust rule all code should be listening to. (Creating locking assymetry always inserts a certain amount of fragility - adding to an already fragile concept here.) And note that there's no reason why text_poke could not be used in stop_machine_run() - the stop_machine_run() handler must not take the text_lock of course - but outside code calling stop_machine_run() can do it and can hence serialize properly. Note that even if we did this then your v2 patch is not fully correct: you need to move the sync_core() at the end of the sequence inside the critical section too. (right now this is mostly harmless because the INVLPG inside the clear_fixmap() happens to be serializing so it has an implicit sync_core() property - but nevertheless we better do this straight away to not cause problems later down the line.) 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/